Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

TOTAL MAXIMUM DAILY LOAD (TMDL) 

For

Total Mercury in Fish Tissue Residue

In the 

Middle & Lower Savannah River Watershed

For Segments

Clarks Hill Lake Dam to Stevens Creek Dam 

Stevens Creek Dam to US Highway 78/278

US Highway 78/278 to Johnsons Landing

Johnsons Landing to Brier Creek

Brier Creek to the Tide Gate

 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

i

TOTAL MAXIMUM DAILY LOAD (TMDL) 

Total Mercury in Fish Tissue Residue

In the 

Middle & Lower Savannah River Watershed

Under the authority of Section 303(d) of the Clean Water Act, 33 U.S.C. 1251 et seq., as amended by the 

Water Quality Act of 1987, P.L. 100-4, the U.S. Environmental Protection Agency is hereby establishing a 

TMDL for total mercury for the protection of public health associated with the consumption of fish taken 

from the following segments of the Savannah River in Georgia:

Clarks Hill Lake Dam to Stevens Creek Dam

Stevens Creek Dam to US Highway 78/278

US Highway 78/278 to Johnsons Landing

Johnsons Landing to Brier Creek

Brier Creek to the Tide Gate

The calculated allowable load of mercury that may come into the identified segments of the 

Savannah River without exceeding the applicable water quality standard of 2.8 nanograms per 

liter is 32.8 kilograms per year. EPA interpreted the State of Georgia’s narrative water quality standard 

for toxic substances for the protection of public health to determine the applicable water quality standard. 

Based on a current estimated loading of 58.8 kilograms per year, an estimated 44% reduction in mercury 

loading is needed for the identified sections of the Savannah River to meet the applicable water quality 

standard of 2.8 nanograms per liter. It is estimated that reductions in air deposition of mercury will result in 

a 38% to 48% reduction in mercury loading to the Savannah River. Twenty-nine (29) facilities permitted by 

the State of Georgia under the National Pollutant Discharge Elimination System Program are provided 

wasteload allocations in this TMDL. 

This TMDL shall become effective immediately, and is incorporated into the Continuing Planning Process 

for the State of Georgia under Sections 303(d)(2) and 303(e) of the Clean Water Act.

Signed this _________ day of___________, 2001.

_____________________________

Beverly H. Banister, Director

Water Management Division
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

ii

Table of Contents

1. Executive Summary................................................................................................................... 1

2. Introduction.............................................................................................................................. 5

3. Phased Approach to the TMDL................................................................................................ 7

3.1. Phased Approach to Atmospheric Sources........................................................................ 8

3.2. Phased Approach to Water Point Sources......................................................................... 9

4. Problem Definition................................................................................................................... 12

4.1. Health Effects of Mercury................................................................................................ 13

5. Applicable Water Quality Standard ......................................................................................... 14

6. Background ............................................................................................................................ 19

6.1. Mercury Cycling ............................................................................................................. 22

6.2. Source Assessment ......................................................................................................... 26

6.2.1. Sources of Mercury...............................................................................................27

6.2.2. Water Point Sources..............................................................................................28

6.3. RELMAP Mercury Deposition Rates.............................................................................. 29

6.4. Available Monitoring Data............................................................................................... 31

6.4.1. EPA Region 4 Data................................................................................................32
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

iii

6.4.2. Water Column Data...............................................................................................34

6.4.3. Sediment Data .......................................................................................................35

6.4.4. Watershed Soil Data..............................................................................................36

6.4.5. Fish Tissue Data.....................................................................................................37

7. Model Development................................................................................................................ 40

7.1. Watershed Hydrologic and Sediment Loading Model....................................................... 40

7.2. Water Quality Fate and Transport Model........................................................................ 41

8. Total Maximum Daily Load (TMDL)....................................................................................... 42

8.1. Critical Condition Determination...................................................................................... 42

8.2. Seasonal Variation.......................................................................................................... 43

8.3. Margin of Safety............................................................................................................. 44

9. TMDL Development............................................................................................................... 45

9.1. Model Results................................................................................................................. 45

9.1.1. Nonpoint Source....................................................................................................46

9.1.2. Water Quality Model.............................................................................................48

9.2. TMDL Determination...................................................................................................... 55

10. Allocation of Loads............................................................................................................. 56
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

iv

10.1. Atmospheric Reductions.............................................................................................. 57

10.2. Allocation to NPDES Point Sources............................................................................ 60

10.3. State and Federal Responsibility.................................................................................. 69

11. Assumptions with Respect to Loadings from South Carolina................................................. 70

12. Appendix A........................................................................................................................ 72

13. References.......................................................................................................................... 75
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

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Table of Figures

Figure 1 BAF vs. Length Fish Collection from Savannah Basin......................................................... 18

Figure 2 Savannah Watersheds........................................................................................................ 20

Figure 3 Savannah Watershed Delineation....................................................................................... 21

Figure 4 Savannah Watershed Landuses.......................................................................................... 22

Figure 5 Mercury Cycling in the Aquatic Environment ...................................................................... 26

Figure 6 Mercury Dry Deposition Rates as Reported in the Mercury Report to Congress................. 30

Figure 7 Mercury Wet Deposition Rates as Reported in the Mercury Report to Congress................. 31

Figure 8 Savannah Watershed Water Column Sample Locations...................................................... 33

Figure 9 Savannah Watershed Fish Collection Locations.................................................................. 34

Figure 10 Model Predictions versus Observed Data for the Savannah River for Drought Conditions.. 52

Figure 11 Model Predictions versus Observed Data for Total Mercury in the Sediments during Low Flow

............................................................................................................................................... 53

Figure 12 Model Predictions versus Observed Data for the Savannah River for Annual Average Flow54

Figure 13 Model Predictions versus Observed Data for Total Mercury in the Sediments Annual Average 

Flow....................................................................................................................................... 55
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

vi

Table of Tables

Table 1 Georgia Department of Natural Resources Fish Consumption Guideline ............................... 12

Table 2 Fish Tissue Analysis............................................................................................................ 19

Table 3 Summaries of Mercury Emissions in the RGM Airshed during the Baseline Period (1994-1996)28

Table 4 Water Column Mercury Concentrations.............................................................................. 35

Table 5 Sediment Mercury Concentrations ...................................................................................... 36

Table 6 Mercury Concentrations in Soils from Surround Watershed................................................. 36

Table 7 Fish Tissue Mercury Data................................................................................................... 37

Table 8 Annual Average Total Mercury Load.................................................................................. 47

Table 9 Specified and Calculated Reaction Rates and Coefficients.................................................... 49

Table 10 Flows, Depths, Velocities and Volumes used in WASP Model.......................................... 50

Table 11 NPDES Permitted Facilities and Assigned Wasteload Allocation at 2.8 ng/l....................... 62
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

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1. Executive Summary

The U.S. Environmental Protection Agency (EPA) Region 4 is establishing this Total Maximum Daily Load 

(TMDL) for total mercury in the middle/lower Savannah River Basin for the 5 contiguous segments of the 

Savannah River from the Clarks Hill Lake Dam to the Tide Gate. The segments are as follows: 

• Clarks Hill Lake Dam to Stevens Creek Dam 

• Stevens Creek Dam to US Highway 78/278

• US Highway 78/278 to Johnsons Landing

• Johnsons Landing to Brier Creek

• Brier Creek to the Tide Gate

Four of these segments are listed on the State of Georgia’s 2000 Section 303(d) list of impaired waters 

because mercury in certain species of fish tissue exceeds the the Georgia Department of Natural Resources 

(GDNR) Fish Consumption Guidelines State’s guidelines. The fifth segment, Johnsons Landing to Brier 

Creek, was inadvertently omitted from the State of Georgia’s 2000 Section 303(d) list. This segment is 

impaired based on GDNR Fish Consumption Guidelines, and the Georgia Environmental Protection 

Division intends to include this segment on the State’s 2002 Section 303(d) List (personal communication, 

Mork Winn, February 27, 2001). Therefore, this TMDL identifies the allowable annual load of total 

mercury for the middle/lower Savannah River from Clarks Hill Dam to the Tide Gate that will result in 

attainment of the applicable water quality standard, and the unrestricted use of these segments for fish 

consumption. 

This TMDL satisfies a consent decree obligation established in Sierra Club, et. al. v. EPA Civil Action, 1: 

94-CV-2501-MHS. The State of Georgia requested EPA to develop this TMDL for the impaired 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

2

segments of the Savannah River, and as such, EPA is establishing this TMDL for Georgia for the 5 

segments of the Savannah River. Although the mid-line of the Savannah River serves as the east-west 

boundary between the states of Georgia and South Carolina, the TMDL does not provide wasteload 

allocations to South Carolina NPDES facilities. This TMDL reflects assumptions that concentrations of 

mercury in the South Carolina portion of the Savannah River will meet the applicable Georgia water quality 

standards at the South Carolina-Georgia border.

 EPA originally proposed this TMDL for total mercury for the middle and lower Savannah River between 

Clarks Hill Dam and the Tide Gate on February 8, 2000. In response to significant comments received 

during the public comment period, the TMDL was revised and re-proposed on December 8, 2000. This 

public comment period closed on January 22, 2001. By establishing this TMDL at this time, EPA is 

satisfying a court-order to finalize this TMDL by February 28, 2001. This TMDL is being established in

phases with this TMDL document representing the first phase of the process. EPA expects to develop a 

revised TMDL for mercury for the middle/lower Savannah River in 2004. EPA believes that a phased 

approach is appropriate for this TMDL because information on the actual contributions of mercury to the 

Savannah River from both point and nonpoint sources will be much better characterized in the future. 

In order for this TMDL to be developed, the applicable water quality standard must be determined. The 

State of Georgia does not have a numeric water quality standard for the protection of public health from 

total mercury. EPA determined that Georgia’s numeric water quality standard for protection of aquatic life, 

12 nanograms per liter (ng/l), is not protective of human health. Based on site-specific field data from the 

middle/lower Savannah River, ambient concentrations of total mercury in the water column are well below 

12 ng/l yet concentrations of mercury in fish tissue exceed levels protective of public health. Therefore, EPA 

does not regard the State’s aquatic life criterion as the applicable water quality standard for this TMDL. 

Instead, EPA has derived a numeric interpretation of the State of Georgia’s narrative water quality standard 

for toxic substances (Chapter 391-3-6-.03 Section (5)(e)) using EPA’s Methodology for Deriving Ambient 

Water Quality Criteria for the Protection of Human Health (EPA 2000). Using recommended national 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

3

values, and site-specific data collected in the middle/lower Savannah River Basin, EPA interpreted 

Georgia’s water quality standard and has determined that the applicable water quality standard for total 

mercury in the ambient water of the Savannah River Basin is 2.8 ng/l (parts per trillion). At this 

concentration, or below, fish tissue residue concentrations of mercury will not exceed 0.4 mg/kg, which is 

protective of the general population from the consumption of freshwater fish. This interpretation of 

Georgia’s water quality standard was based on site-specific data gathered for the Savannah River in 2000 

specifically for the purpose of this TMDL. It does not apply to any other water in the State of Georgia. In 

addition, in any future TMDLs for Savannah River, it is possible that EPA may revise this interpretation 

based on new site-specific data collected at that time. 

During the time that this TMDL was proposed and was in public review between December 8, 2000, and 

January 22, 2001, EPA issued federal criterion recommendations for methylmercury on December 30, 

2000. (See Water Quality Criteria for Protection of Human Health: Methylmercury, EPA-823-F-01-001.) 

 This document recommends 0.3 mg/kg as a fish tissue residue concentration for protection of human health. 

 Since EPA was under court order to finalize this TMDL by February 28, 2001, EPA had insufficient time 

to consider the new federal criterion recommendations in the establishment of this TMDL. Therefore, EPA 

may reconsider this TMDL at some future date (prior to 2004) in order to consider the new federal criterion 

guidance in the context of this waterbody. It should be noted, however, that today’s TMDL protects the 

designated uses and achieves the applicable water quality standard as interpreted by EPA. In order to 

assure protection, EPA made conservative assumptions in this TMDL in the derivation of the applicable 

water quality standard, particularly relating to the bioaccumulation factor (BAF). EPA assumed that all 17.5 

grams per day of fish consumed are of largemouth bass, which as a trophic level 4 fish, bioaccumulates 

mercury at comparatively high rates. (This means that consumers of these fish will be exposed to more 

mercury than would be the case if they consumed lower trophic level fish species.) The resulting water 

quality standard as interpreted by EPA appears to be as protective as the numeric value EPA would have 

derived using the recommended assumptions in the Human Health Methodology (a “weighted” BAF rather 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

4

than a trophic level 4 BAF; a general population consumption rate of 17.5 grams per day; a methylmercury 

reference dose of 0.0001 mg/k/day; and a relative source contribution dose of 0.00027 mg/kg/day). This 

conclusion depends on the appropriate “weighted BAF” value, which will be considered in any future 

revision of this TMDL.

Computerized modeling techniques have been employed in the development of this TMDL. The loading of 

mercury from the watershed into the Savannah River was simulated using a Watershed Characterization 

System (WCS) model developed by EPA Region 4 (USEPA, Region 4, 2001). The WCS provides a 

simplified simulation of precipitation-driven runoff and sediment delivery. Solids load from runoff is used to 

estimate pollutant delivery to the River from the watershed. The water quality model known as WASP5 

(Ambrose, et al., 1993) is used to simulate mercury fate and transport in the Savannah River. WASP5 is a 

general dynamic mass balance framework for modeling contaminant fate and transport in surface waters.

EPA evaluated the current loading conditions and calculated the water column concentration using the 

modeling approach described in this document. The calculated allowable load of mercury that can 

come into the Savannah River without exceeding the applicable water quality standard as 

interpreted by EPA of 2.8 ng/l is 32.8 kilograms/year. Because this assessment indicates that 99% of 

the loading of mercury is from atmospheric sources, 99% of the allowable load will be assigned to the load 

allocation, and 1% of the available load will be assigned to the wasteload allocation. Therefore, the Load 

Allocation and Wasteload Allocation for the middle/lower Savannah River are:

Load Allocation (atmospheric sources) = 0.99 (32.8) = 32.5 kilograms/year

Wasteload Allocation (NPDES sources) = 0.01 (32.8) = 0.3 kilograms/year

The estimated current loading of mercury to the Savannah River from the surrounding watershed is 58.8 

kilograms/year. This load was determined by adding the predicted mercury load for each of the 

subwatersheds taking into account delivery times and volatilization that occurs in the tributaries. The 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

5

difference between the estimated current mercury load (58.8 kg/year) and the calculated allowable load 

(32.8 kg/year) is 26 kilograms/year. Since 32.8 kg/year is 56% of the estimated current loading of 

mercury, it is estimated that a 44% reduction in total mercury loading is needed for the middle/lower 

Savannah River to achieve a water column concentration of 2.8 ng/l. 

An analysis conducted by the EPA Region 4 Air Program concludes that an estimated 38% to 48% 

reduction in mercury deposition to the Savannah Watershed can be achieved by 2010. EPA expects these 

reductions to be achieved through full implementation of the current Clean Air Act (CAA) Section 112 

Maximum Achievable Control Technology (MACT) requirements, Section 111 New Stationary Source 

Standards, and Section 129 Solid Waste Combustion requirements at sources within the local airshed. 

(USEPA, 2000)

This TMDL assigns a cumulative wasteload allocation (WLA) to all NPDES point sources of 0.3 kilograms 

per year. This TMDL assumes that this cumulative WLA will be accomplished through the imposition of 

numeric water quality-based permit limits or through the implementation of mercury minimization plans at 

appropriate NPDES facilities. The wasteload allocation options for NPDES permitted facilities are 

described in Section 10. 

2. Introduction

The U.S. Environmental Protection Agency (EPA) Region 4 is establishing this Total Maximum Daily Load 

(TMDL) for total mercury for the middle/lower Savannah River from the Clarks Hill Lake Dam to the Tide 

Gate. The segments are as follows: 

• Clarks Hill Lake Dam to Stevens Creek Dam 

• Stevens Creek Dam to US Highway 78/278

• US Highway 78/278 to Johnsons Landing
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

6

• Johnsons Landing to Brier Creek

• Brier Creek to the Tide Gate

Four of these segments are listed on the State of Georgia’s 2000 Section 303(d) list of impaired waters 

because mercury in certain species of fish tissue exceeds the the Georgia Department of Natural Resources 

(GDNR) Fish Consumption Guidelines State’s guidelines. The fifth segment, Johnsons Landing to Brier 

Creek, was inadvertently omitted from the State of Georgia’s 2000 Section 303(d) list. This segment is 

impaired based on GDNR Fish Consumption Guidelines, and the Georgia Environmental Protection 

Division intends to include this segment on the State’s 2002 Section 303(d) List (personal communication, 

Mork Winn, February 27, 2001). 

TMDLs are required for waters on a state’s Section 303(d) list by Section 303(d) of the Clean Water Act 

(CWA) and the associated regulations at 40 CFR Part 130. A TMDL establishes the maximum amount of 

a pollutant a waterbody can assimilate without exceeding the applicable water quality standard. The TMDL 

allocates the total allowable pollutant load to individual sources or categories of pollution sources through 

wasteload allocations (WLAs) for point sources regulated by the National Pollutant Discharge Elimination 

System (NPDES) program and through load allocations (LAs) for all other sources. The WLAs and LAs in 

the TMDL provide a basis for states to reduce pollution from both point and nonpoint sources that will lead 

to restoration of the quality of the impaired waterbody. The purpose of this TMDL is to identify the 

allowable load of mercury that will result in attainment of the applicable water quality standard as interpreted 

by EPA, and the unrestricted use of the identified segments for fish consumption. 

 This TMDL satisfies a consent decree obligation established in Sierra Club, et. al. v. EPA, Civil Action: 94-

CV-2501-MHS. The Consent Decree requires TMDLs to be developed for all waters on Georgia’s 

current Section 303 (d) list consistent with the schedule established by Georgia for its rotating basin 

management approach. The State of Georgia requested EPA to develop this TMDL, and as such, EPA is 

establishing this TMDL for Georgia for the 5 segments of the Savannah River. Although the mid-line of the 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

7

Savannah River serves as the east-west boundary between the states of Georgia and South Carolina, the 

TMDL does not provide wasteload allocations to South Carolina NPDES facilities. This TMDL reflects 

assumptions that concentrations of mercury in the South Carolina portion of the Savannah River will meet 

the applicable Georgia water quality standards as interpreted by EPA at the South Carolina-Georgia 

border.

On February 8, 2000, EPA originally proposed this TMDL for total mercury for the segments of the 

Savannah River listed on the State of Georgia’s 1998 Section 303(d) List. During the public comment 

period on that proposed TMDL which closed April 10, 2000, EPA received extensive and significant 

comments on the TMDL. As a result, EPA obtained an extension of the schedule to finalize the TMDL 

from June 7, 2000 to February 28, 2001. This TMDL satisfies the court-ordered commitment. 

3. Phased Approach to the TMDL

EPA recognizes that it may be appropriate to revise this TMDL based on information gathered and analyses 

performed after February 2001. With such possible revisions in mind, this TMDL is characterized as a 

phased TMDL. In a phased TMDL, EPA or the state uses the best information available at the time to 

establish the TMDL at levels necessary to implement applicable water quality standards and to make the 

allocations to the pollution sources. However, the phased TMDL approach recognizes that additional data 

and information may be necessary to validate the assumptions of the TMDL and to provide greater certainty 

that the TMDL will achieve the applicable water quality standard. Thus, the Phase 1 TMDL identifies data 

and information to be collected after the first phase TMDL is established that would then be assessed and 

would form the basis for a Phase 2 TMDL. The Phase 2 TMDL may revise the needed load reductions or 

the allocation of the allowable load or both. EPA intends to gather new information and perform new 

analyses so as to produce a revised or Phase 2 TMDL for mercury for the identified segments of the 

Savannah River, if necessary, in 2004. The phased approach is appropriate for this TMDL because 

information on the actual contributions of mercury to the Savannah River from both point and nonpoint 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

8

sources will be much better characterized in the future. 

3.1. Phased Approach to Atmospheric Sources

The impairment of the Savannah River by mercury is largely due to the deposition of mercury from the 

atmosphere. This TMDL estimates that approximately 99 percent of the pollutant loads to the River come 

from the atmosphere (Table 8). An analysis of atmospheric deposition to the Savannah River watershed is 

included in this TMDL as Appendix A. Mercury is emitted into the atmosphere by a large number of 

different sources. The mercury that reaches the Savannah River watershed comes from nearby sources 

(local sources) as well as sources much farther away, both within the United States (national sources) and 

outside of the United States (international sources). Only a small part, approximately 1 percent, of the 

mercury loading into the Savannah River is due to discharges from water point sources (e.g., pipes) into the 

Savannah River or its tributaries. 

In Appendix A, EPA has made its best attempt to characterize the air sources of mercury to the watershed, 

given the time available to the Agency for establishing the TMDL. The analysis of deposition of mercury 

from the atmosphere to the Savannah watershed depends heavily on modeling conducted for the Mercury 

Study Report to Congress (EPA, 1997). This Study was based on the Regional Lagrangian Model of Air 

Pollution (RELMAP) modeling, which has several areas of uncertainty, and assumptions that could affect 

the level of reductions projected by the analysis. Many of these uncertainties are not unique to the analysis 

of atmospheric deposition prepared for the Savannah River Mercury TMDL. Some of these uncertainties 

include the estimates of the amount of the chemical form or species of mercury emitted by each source 

category; the projected level of reductions from each source category subject to the Clean Air Act (CAA) 

Section 129 or 111 or MACT; the definition of local sources contributing deposition to the watershed; the 

contribution from global sources; and other aspects of the modeling. While it is not possible to quantify the 

net effect of these factors, EPA believes the assumptions made to address these uncertainties are reasonable 

and consistent with the state-of-the art mercury modeling available at the time this TMDL was prepared and 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

9

that the agency has reasonable assurance that needed air reductions will be achieved. Nonetheless, it is 

important to point out that, because of these uncertainties, the anticipated 38% to 48% reductions in 

atmospheric deposition reported in this TMDL are an estimate only. 

EPA expects that emissions of mercury from air sources (and consequently deposition of mercury to the 

Savannah River) will continue to be reduced during the first phase of this TMDL through implementation of 

the CAA’s MACT and Section 129 and Section 111 regulations. In addition, EPA expects reductions in 

the air emissions of mercury may be achieved through implementation of voluntary programs. At the same 

time, EPA is considering additional regulatory actions under the CAA that may result in further reductions of 

mercury emissions from air sources. EPA is also undertaking new computer modeling that will allow a better 

characterization of sources contributing to the deposition of mercury and, therefore, more certainty 

regarding the extent of mercury reductions that can be achieved in a watershed from air sources. By 2004, 

when EPA expects to revise the TMDL, this additional modeling information and estimates of additional 

future reductions will be available, allowing EPA to validate the assumptions and verify the anticipated 

reductions in loadings and revise the TMDL accordingly. 

3.2. Phased Approach to Water Point Sources

At this time, there is relatively little data on the actual loading of mercury from NPDES point sources in the 

basin. Because, until recently, EPA’s published method for the analysis of mercury was not sensitive 

enough to measure mercury at low trace level concentrations, most NPDES facilities have not detected 

mercury during their required priority pollutant monitoring. EPA assumes, however, that all facilities 

discharge some mercury into the River with their effluent because mercury is pervasive in the environment 

and is present in rainwater. 

Recently, in 1998, EPA adopted a new analytical procedure that detects mercury at low trace level 

concentrations (0.5 nanograms/liter) (See EPA Method 1631, Revision B, 40 C.F.R. 136.3(a)). A 

sampling by EPA of a small subset of the NPDES dischargers in Georgia in the Savannah River Basin using 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

10

the trace level Method 1631 analytical technique verifies EPA’s assumption that all facilities are discharging 

some mercury. As NPDES permits are reissued, dischargers will be required to use the version of Method 

1631 then in effect for analyzing mercury. (Georgia Rules and Regulations for Water Quality Control, 

Chapter 391-3-6-.06). Therefore, in the Phase 2 TMDL, data on the concentration of mercury in point 

source discharges using the more sensitive analytical technique will be available to characterize the actual 

loading of mercury into the Savannah River. This will allow EPA, as appropriate, to refine wasteload 

allocations provided in the TMDL.

Other circumstances may also influence the wasteload allocations that are established in the second phase of 

this TMDL. As an example, EPA issued criterion guidance for methylmercury on December 30, 2000. 

(See Water Quality Criteria for Protection of Human Health: Methylmercury, EPA-823-F-01-001.) This 

new guidance was issued after this TMDL was proposed on December 8, 2000, and is not incorporated 

into the development of this TMDL. However, the Federal Register notice announcing the availability of the 

new methylmercury criterion guidance explains that EPA expects the states to use the federal criterion as 

guidance in updating their water quality standards. EPA expects states to adopt a new or revised water 

quality criterion for methylmercury at levels necessary to protect human health. The State of Georgia will be 

undertaking a review of their water quality standards within the next 3 years; therefore, EPA anticipates that 

by 2004 Georgia will have adopted a numeric human health criterion for methylmercury. The revised 2004 

TMDL will be based on the State’s numeric human health criterion for mercury, if such criterion exists, 

rather than on EPA’s interpretation of the State’s narrative water quality standard for toxic substances as 

was done in this Phase 1 TMDL (See Section 5).

Because the impairment of the Savannah River by mercury is due predominantly to air deposition, the 

complete elimination or significant reduction of mercury from water point source discharges would produce 

little benefit in the quality of the Savannah River. In addition, the elimination or significant reduction of 

mercury would likely be expensive and possibly technically infeasible for point sources to implement. Since 

many of the NPDES facilities in the basin affected by this TMDL are municipal wastewater treatment plants 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

11

that are funded through the taxpayers, EPA chooses to move cautiously before implementing wasteload 

allocations that may cause significant economic hardship in a situation where, as here, EPA expects most of 

the needed mercury reductions to be achieved through Clean Air Act reductions in mercury emissions from 

air sources. In this Phase 1 TMDL, EPA expects point source loadings of mercury will be reduced 

primarily through mercury minimization programs developed and implemented by some point sources. 

In summary, during implementation of the Phase 1 TMDL, EPA expects the following activities to occur:

• 29 NPDES facilities will monitor for mercury and characterize it in their influent and effluent for 

mercury using the more sensitive analytical technique (the version of Method 1631 then in effect). 

These facilities consist of 15 municipal facilities, and 14 industrial facilities. (See Section 10.2.)

• Where appropriate, NPDES point sources will develop and implement mercury minimization plans;

• Air point sources will continue to reduce emissions of mercury through implementation of the Clean 

Air Act Section 112 MACT requirements and Section 129 Solid Waste Combustion requirements;

• EPA and the regulated community will improve the mercury air emissions inventory;

• EPA will refine and revise the mercury air deposition modeling to better characterize sources of 

mercury; and

• EPA and the states will collect additional ambient data on mercury concentrations in water, 

sediment and fish.

• EPA expects Georgia to adopt a numeric water quality criterion for methylmercury for the 

protection of human health that is based on EPA’s recent criteria guidance, either as published or as 

modified to reflect site-specific conditions, or that are based on other scientifically defensible 

methods. (See 40 C.F.R. 131.11(b))
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

12

EPA intends to use the data and information collected and developed during the next four years to revise the 

Phase 1 TMDL, as necessary, to assure that EPA’s interpretation of the State’s applicable water quality 

standard is appropriate, and that the allowable load will be achieved by implementation of the TMDL. 

EPA’s intention to revise the TMDL is consistent with the State of Georgia’s Rotating Basin Management 

Program (RBMP) schedule. Under Georgia’s current RBMP schedule, NPDES permits in the Savannah 

River Basin will be reissued in 2005. Therefore, EPA intends to revise the TMDL one year prior to 

reissuance of permits in the Savannah River Basin. 

4. Problem Definition

The water segments in the Savannah River Basin for which this proposed TMDL is being established are 

listed on the State of Georgia’s 2000 Section 303(d) list except Johnsons Landing to Brier Creek (Johnsons 

Creek to Brier Creek is impaired and will be listed on the State’s 303(d) List, See Section 2). The waters 

were listed (and Johnsons Landing to Brier Creek will be listed) because mercury in the tissue of several 

species of fish exceeds the Fish Consumption Guidelines (FCG) established by the State of Georgia. (See 

Georgia Department of Natural Resources, 2000.) The Fish Consumption Guidelines establish limits on the 

amount of fish that should be consumed over a given time frame (a week or a month) in order to protect 

human health. 

The Georgia Department of Natural Resources (DNR) uses a risk-based approach to determine how often 

contaminated fish may be consumed at different levels of fish tissue contamination assuming a consumption 

rate of approximately 32.5 grams per day. Table 1 provides the frequency of consumption for three 

different levels of fish tissue contamination with mercury.

Table 1 Georgia Department of Natural Resources Fish Consumption Guideline

Mercury Fish Tissue 

Threshold (mg/kg)

Frequency of 

Consumption 

0.23 Once a Week
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

13

0.70 Once a Month

2.3 Do Not Eat

If fish tissue contains 0.23 mg/kg (parts per million) or more mercury, the State’s FCG indicates that the fish 

should not be consumed more than once a week. If fish tissue contains 0.70 mg/kg (parts per million) or 

more mercury, the State’s FCG indicates the fish should not be consumed more than once a month, and if 

the fish tissue contains 2.30 mg/kg (parts per million) or greater of mercury, the State issues a “Do Not Eat” 

guideline. 

The following FCG are in place for the segments of the Savannah River covered by this TMDL: 1) 

Columbia County - 1 meal per week for largemouth bass and spotted sucker, 2) Richmond/Burke Counties 

- 1 meal per week for largemouth bass, 3) Screven County - 1 meal per week for largemouth bass, 4) 

Effingham County - 1 meal per month for largemouth bass, 5) Fort Howard - 1 meal per week for white 

catfish and 1 meal per month for largemouth bass and bowfin, 6) Chatham County - 1 meal per week for 

largemouth bass, and 7) Tidal Gate - 1 meal per week for white catfish. 

4.1. Health Effects of Mercury

The State of Georgia’s fish consumption guideline program is designed to protect consumers in Georgia 

from the health effects of mercury consumed through fish in the diet. Human exposure to inorganic mercury 

in large amounts can cause a variety of health effects. The two organ systems most likely affected by 

methylmercury are the central nervous system and the kidney. However, the most significant concerns 

regarding chronic exposure to low concentrations of methylmercury in fish are for neurological effects in the 

developing fetus and children. 

EPA recently issued national advisory concerning risks to children and to pregnant or nursing women 

associated with mercury in freshwater fish caught by their friends and family. (See EPA Consumption 

Advisory: Advice for Women and Children on Non-commercial Fish Caught by Friends and Family, EPA823-F-01-004, January 2001.) The groups most vulnerable to the effects of mercury pollution include: 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

14

women who are pregnant or may become pregnant, nursing mothers, and young children. To protect against 

the risks of mercury in fish caught in freshwaters, EPA is recommending that these groups limit fish 

consumption to one meal per week for adults (6 ounces of cooked fish, 8 ounces uncooked fish) and one 

meal per week for young children (2 ounces cooked fish or 3 ounces uncooked fish). The National 

Academy of Sciences confirms that methylmercury is a potent toxin and concludes that the babies of women 

who consume large amounts of fish when pregnant are at greater risk for changes in their nervous system 

that can affect their ability to learn. (NAS, Toxicological Effects of Methylmercury, July 2000) EPA is 

issuing this advice for women who are pregnant or may become pregnant, nursing mothers, and young 

children to raise awareness of the potential harm that high levels of methylmercury in fish can cause to a 

baby or child’s developing brain and nervous system. This advice provides guidance on the amount of fish 

caught by friends and family that these groups can eat to keep methylmercury from reaching harmful levels.

The purpose of this TMDL is to establish the acceptable loading of mercury from all sources, such that 

mercury levels in the middle/lower Savannah River will not exceed the applicable water quality standard as 

interpreted by EPA for protection of public health. If concentrations in the River can be reduced to the 

applicable water quality standard as interpreted by EPA (expressed in terms of ambient water column 

concentrations), fish tissue levels of mercury will decrease over time. Eventually, fish tissue levels of 

mercury should become low enough that consumers may eat unlimited quantities of fish from the River 

without fear of health effects. 

5. Applicable Water Quality Standard

TMDLs are established at levels necessary to attain and maintain the applicable narrative and numerical 

water quality standards. (See 40 CFR Section 130.7(c)(1).) The State of Georgia’s Rules and Regulations 

for Water Quality Control do not include a numerical water quality standard for human health for total 

mercury. The only mercury criterion provided in State regulations is 12 ng/l for protection of aquatic life

from total mercury. EPA recognizes that the derivation of a human health criterion for mercury is more 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

15

complex than most metals because of the methylation of mercury that occurs in the aquatic environment. 

(See Ambient Water Quality Criteria for Mercury Document, EPA, 1986) Like the current criteria 

guidance, the 1986 criterion document recommends that fish tissue be analyzed to determine whether the 

concentration of methylmercury exceeds the level necessary to protect human health. The document 

acknowledges that a 12 ng/l aquatic life criterion, while protecting the health of the fish themselves, may not 

prevent the unacceptable bioaccumulation of mercury in fish tissue, which would adversely affect the health 

of humans consuming the fish. 

EPA collected site-specific data on ambient mercury in the water column and fish tissue from the Savannah 

River which indicate the 12 ng/l aquatic life criterion is not protective of human health. In July 2000, EPA 

collected samples of ambient water at 10 locations in the mainstem and 6 locations in tributaries to the 

Savannah River from below Clarks Hill Dam to the Tide Gate. Total mercury concentrations in the water 

ranged from 0.27 ng/l to 9.50 ng/l. These concentrations of mercury are well below the State’s 12 ng/l 

aquatic life criterion. However, the average fish tissue residue concentration from 13 of the 16 sampling 

locations exceeds 0.23 mg/kg. Thus, at water concentrations below 12 ng/l (significantly below in most 

instances), fish tissue is accumulating mercury at levels above the State’s Fish Consumption Guidelines 

indicating that a water concentration of 12 ng/l is not protective of human health. 

Since the State lacks a numeric water quality criterion for the protection of human health, EPA has 

interpreted the State’s narrative water quality standard for toxic substances (Chapter 391-3-6-.03 Section 

(5)(e)) to identify a water concentration sufficient to protect the human health designated use. In order to 

use the best available, sound science in interpreting this narrative, EPA used the Methodology for Deriving 

Ambient Water Quality Criteria for the Protection of Human Health (EPA 2000) to derive the applicable 

water quality standard for this TMDL. This standard as interpreted by EPA is the maximum concentration 

of mercury that can be present in the water column without causing a fish tissue residue concentration that 

poses adverse health effects.
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

16

Using EPA’s Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health 

(referred to as EPA’s Human Health Methodology), EPA determined that a 0.4 mg/kg fish tissue residue 

value will protect the general population from the adverse health effects of mercury due to the consumption 

of freshwater fish. To interpret Georgia’s Water Quality Standards, EPA assumed that the general 

population consumes 17.5 grams per day of large mouth bass, a trophic level 4 fish. EPA is using 0.4 

mg/kg in fish tissue as the appropriate “end point” upon which to base the interpretation of the applicable 

water quality standard. 

To calculate the maximum water column concentration that will not allow mercury to bioaccumulate in fish 

tissue to above 0.4 mg/kg, the EPA Human Health Methodology is again applied. The methodology is 

expressed below:

( * * )

(Re * * )

ConsumptionRate BAF FractionMeHg

ferenceDose BodyWeight UnitsConversion WQS =

where:

WQS = EPA’s Interpretation of Georgia’s Water Quality Standard

Reference Dose = 0.0001 mg/kg/day MeHg

Body Weight = 70 kg

Units Conversion = 1.0E6

Consumption Rate = 0.0175 kg/day Fish•

Bioaccumulation Factor = 4,000,000 as measured in the Savannah Watershed

Fraction of the Total Mercury as Methylmercury = 0.0353 as measured in the Savannah Watershed

In the calculation, the Region used the recommended national values for most of the factors in the Human 

Health Methodology, including the reference dose of 0.0001-mg/k/day methylmercury; a standard average 

 

• The fish intake value of 17.5 g/day (general adult population) was taken from EPA’s 2000 Revisions to the Methodology 

for Deriving Ambient Water Quality Criteria for the Protection of Human Health (65 FR 66444-66482 (11/3/200)). 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

17

adult body weight of 70 kg; and the consumption rate for the general population of 17.5 grams per day. 

(Note that a recent report by the National Academy of Sciences confirms that methylmercury is a potent 

toxin, and concludes that EPA’s reference dose of 0.0001 mg/kg/day is appropriate (See NAS, 

Toxicological Effects of Methylmercury, July 2000)). For the other factors in the calculation,

bioaccumulation and fraction methylmercury, EPA collected site-specific data from the Savannah River 

Basin in August and September of 2000. (The site-specific data is presented in Section 6.4.) From this 

site-specific data, EPA determined a representative BAF value to be 4,000,000 and a median measured 

percentage methylmercury of 3.53%. Using recommended national values, and factors calculated from sitespecific data, EPA interpreted Georgia’s water quality standard and has determined that the applicable 

water quality standard for total mercury in the ambient water of the middle and lower Savannah River Basin 

is 2.8 ng/l (parts per trillion). This water quality standard, when fully achieved, will prevent the unacceptable 

bioaccumulation of mercury in fish from all segments of the middle/lower Savannah River. This

interpretation of Georgia’s water quality standard was based on site-specific data gathered for the Savannah 

River in 2000 specifically for the purpose of this TMDL. It does not apply to any other water in the State 

of Georgia. In addition, in any future TMDLs for Savannah River, it is possible that EPA may revise this 

interpretation based on new site-specific data collected at that time. 

In determining the applicable water quality standard as interpreted by EPA, it was necessary to determine a 

representative bioaccumulation factor (BAF) as discussed above. It is common to have a large range in 

BAFs calculated from field data collected within the same river system. Figure 1 illustrates the range of 

BAFs calculated for all the fish sampled by EPA in August and September of 2000. The BAFs range from 

less than 1 million to over 18 million. An appropriate BAF for interpreting Georgia’s Water Quality 

Standards was selected from the central tendency of the measured data for a fish 315 millimeter (mm) in 

length. (See Figure 1) EPA is assuming a 305-315 mm fish is representative of the size and age of fish that 

is most likely to be consumed and also represents the minimum length requirement for the fisherman to keep. 

A representative BAF for a 315 mm fish in the Savannah River Basin is 4,000,000. 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

18

Length vs. BAF

0

2000000

4000000

6000000

8000000

10000000

12000000

14000000

16000000

18000000

20000000

150 250 350 450 550 650 750

Length

BAF

Bowfin

Chain Pickerel

Grass Pickerel

Large Mouth Bass

Striper

All Fish

Linear (All Fish)

Figure 1 BAF vs. Length Fish Collection from Savannah Basin

Furthermore, to support the selection of the 4,000,000 BAF value, the individual fish for each segment/tributary 

were analyzed to determine a central tendency BAF that would be protective of the fish species and population that 

this TMDL is being developed to protect. Data collected for the sections of the river and tributaries were analyzed 

and compared statistically. 

Table 2 provides the average BAFs determined for each tributary and segment of the Savannah River Basin 

for which data was collected. This analysis shows that an acceptable BAF would be between 3,255,807 

and 4,604,485. Using this analysis and regression method shown in Figure 1, the selection of 4,000,000 

provides a reasonable estimate of the BAF to be used in the Human Health Methodology calculation.

The site-specific data used to develop the applicable water quality standard was obtained during a one-time 

sampling event in the summer of 2000. EPA intends to revisit its interpretation of Georgia’s water quality 

standard in Phase 2 when more data is available for total mercury in the water column over a longer time 

period and environmental conditions.
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

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Table 2 Fish Tissue Analysis 

River/Tributary Segment

Average 

Fish 

Tissue 

(ppm)

Water 

Column 

Total 

Hg 

(ng/L)

Water 

Column 

MeHg 

 (ng/L)

Fraction 

MeHg

Average 

BAF

Savannah River-Below Clark's Hill Dam 0.251 0.27 0.02 0.078 11,710,280

Savannah River-Below Horse Creek 0.074 0.68 0.10 0.141 768,229

Savannah River-Below Butler Creek 0.316 1.19 0.16 0.131 2,026,871

Savannah River-Below Upper Three Run 0.181 3.27 0.07 0.020 2,744,723

Savannah River-Below Lower Three Run 0.180 9.50 0.06 0.006 3,142,770

Savannah River-Below Brier Creek 0.415 2.80 0.09 0.032 4,703,913

Savannah River-Clyo, USGS Gage 0.633 3.28 0.09 0.027 7,271,958

Savannah River-Below Ebenezer Creek 0.665 3.44 0.08 0.022 8,698,953

Savannah River-Tide Gate (Freshwater) 0.407 4.44 0.09 0.021 4,319,872

Savannah River-Tide Gate (Estuary) 0.389 4.09 0.06 0.015 6,321,951

Horse Creek 0.264 6.16 0.24 0.039 1,096,266

Butler Creek 0.305 2.14 0.39 0.182 780,769

Upper Three Runs Creek 0.783 5.82 0.16 0.027 4,896,829

Lower Three Runs Creek 1.085 2.43 0.13 0.051 8,676,761

Brier Creek 0.493 2.15 0.11 0.050 4,562,963

Ebenezer Creek 1.269 3.34 0.65 0.195 1,948,651

Average 0.482 3.44 0.15 0.065 4,604,485

Median 0.398 3.28 0.10 0.035 4,441,418

Average (Mean) River 0.351 3.30 0.08 0.049 5,170,952

Median River 0.352 3.28 0.08 0.024 4,511,893

Average (Mean) Tributary 0.700 3.67 0.28 0.091 3,660,373

Median Tributary 0.638 2.89 0.20 0.051 3,255,807

6. Background

The middle & lower Savannah River watershed is located in eastern Georgia. The entire drainage area of 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

20

the Savannah watershed (USGS Hydrologic Unit Code (HUC) 3060106, 3060108, 3060109) is 

approximately 9318 square kilometers. The Savannah watershed is presented in Figure 2.

Figure 2 Savannah Watersheds

To develop the TMDL, EPA divided the Savannah watershed into 31 subwatersheds (Figure 3) that 

represent all of the major tributaries to the Savannah River. This TMDL presents a total mercury load for 

each of these subwatersheds in order to determine the impact of atmospheric deposition on the Savannah 

River.
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

21

Figure 3 Savannah Watershed Delineation

The watershed contains several different types of land uses. The landuses for the Savannah River 

watershed are given in Figure 4. Different landuses collect and distribute mercury at different rates as a 

function of runoff and erosion.
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

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Figure 4 Savannah Watershed Landuses

6.1. Mercury Cycling

Mercury chemistry in the environment is quite complex and is not totally understood. Mercury has the 

properties of a metal (including persistence due to its inability to be broken down), but also has some 

properties of a hydrophobic organic chemical due to its ability to be methylated through a bacterial process. 

 Methylmercury is easily taken up by organisms, and will bioaccumulate. It is effectively transferred through 

the food web, magnifying at each trophic level. This can result in high levels of mercury in organisms high on 

the food chain, despite nearly immeasurable quantities of mercury in the water column. In fish, mercury is 

not usually found in levels high enough to cause the fish to exhibit signs of toxicity, but the mercury in sport 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

23

fish can present a potential health risk to humans.

Figure 5 provides a schematic of mercury cycling in the aquatic environment. The boxes represent stores of 

mercury, while the arrows illustrate the various fluxes that control mercury cycling in the environment. The 

top of the diagram summarizes the various forms of mercury that may be loaded into a waterbody. It is 

important to recognize that mercury exists in a variety of forms, including elemental mercury (Hg (0)), ionic 

mercury (Hg (I) & Hg (II)), and compounds in which mercury is joined to an organic molecule. In the 

schematic, Hg (I) is ignored, as Hg (II) generally predominates in aquatic systems. Mercuric sulfide (HgS 

or cinnabar) is a compound formed from Hg (II), but is shown separately, as it is the predominant natural 

ore. Organic forms of mercury include methylmercury (CH3Hg or “MeHg”), and also other organic forms, 

including natural forms such as dimethylmercury and man-made compounds such as organic mercury 

pesticides.

In the aquatic mercury cycle it is critical to consider the distribution of mercury load between the various 

forms. The major forms reaching the water from the watershed can have different behavior:

• Mercuric sulfide (HgS), can be washed into the water as a result of weathering of natural cinnabar 

outcroppings. HgS has low solubility under typical environmental conditions and would be 

expected to settle out to the bottom sediments. However, under aerobic conditions Hg (II) may be 

liberated by a bacteria-mediated oxidation of the sulfide ion. This Hg (II) would then be more 

bioavailable and would be available for methylation. Alternatively, under anaerobic conditions, HgS 

may be formed from Hg (II).

• Methylmercury (MeHg) is found in rainfall and may be found in small amounts in mine tailings or 

sediments. It is more soluble than HgS and has a strong affinity for lipids in biotic tissues.

• Elemental mercury (Hg (0)), may remain in mine tailings, as has been noted in tailings piles from 

recent gold mining in Brazil. Elemental mercury tends to volatilize into the atmosphere, though some 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

24

can be oxidized to Hg (II).

• Other mercury compounds contain and may easily release ionic Hg (II). Such compounds are 

found in the fine residue left at abandoned mine sites where mercury was used to extract gold or 

silver from pulverized rock.

Dimethylmercury is ignored in the schematic because this species seems to occur in measurable quantities 

only in marine waters. Organic mercury pesticides also have been ignored in this TMDL study since such 

pesticides are not currently used in this country and past use is probably insignificant.

Mercury and methylmercury form strong complexes with organic substances (including humic acids) and 

strongly sorb onto soils and sediments. Once sorbed to organic matter, invertebrates can ingest mercury. 

Some of the sorbed mercury will settle to the bottom, and if buried deep enough, mercury in the bottom 

sediments will become unavailable to cycle. Burial in bottom sediments can be an important route of 

removal of mercury from the aquatic environment. 

Methylation and demethylation play an important role in determing how mercury will accumulate through the 

food web. A biological process that appears to involve sulfate-reducing bacteria may result in methylated 

Hg (II). Rates of biological methylation of mercury can be affected by a number of factors. Methylation 

can occur in water, sediment and soil solution under anaerobic conditions and to a lesser extent under 

aerobic conditions. In water, methylation occurs mainly at the sediment-water interface and at the oxicanoxic boundary within the water column. The rate of methylation is affected by the concentration of 

available Hg (II) (which can be affected by the concentration of certain ions and ligands), the microbial 

concentration, pH, temperature, redox potential, and the presence of other chemical processes. 

Methylation rates appear to increase at lower pH. Bacteria also cause demethylation of mercury.

Note in Figure 5 that both Hg (II) and methylmercury (MeHg) sorb to algae and detritus, but only the 

methylmercury is assumed to be passed up to the next trophic level. Invertebrates eat algae and detritus, 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

25

thereby accumulating any MeHg that has sorbed to these constituents. Fish eating the invertebrates and 

either growing into larger fish (which have been shown to have higher body burdens of mercury) or eaten by 

larger fish will then bioaccumulate mercury. At each trophic level, a bioaccumulation factor must be 

assumed to represent the magnification of mercury that occurs as one moves up the food chain.

Typically, almost all of the mercury found in fish (greater than 95%) is in the methylmercury form. Studies 

have shown that fish body burdens of mercury increase with increasing size or age of the fish, with no signs 

of leveling off. 

Although it is important to identify sources of mercury to the waterbody, there may be fluxes of mercury 

within the waterbody that would continue nearly unabated for some time even if all the sources in the 

watershed and waterbody were eliminated. In other words, compartments within the watershed and 

waterbody store significant amounts of mercury, and this mercury can continue to cycle through the system 

even without an ongoing source of mercury. The most important store of mercury is likely the river 

sediments and the surrounding swamps and marshes. The mercury in these pools may cause exposure to 

biota by being:

• Resuspended into the water column, where it is ingested or adsorbs to organisms that are later 

ingested.

• Methylated by bacteria. The methylmercury tends to attach to organic matter, which may be 

ingested by invertebrates and thereby introduced to the food web. It is methylmercury that poses 

the real threat to biota due to its strong tendency to accumulate in biota and magnify up the food 

chain.
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

26

Figure 5 Mercury Cycling in the Aquatic Environment

6.2. Source Assessment

A TMDL evaluation examines the known potential sources of the pollutant in the watershed, including point 

sources, nonpoint sources, and background levels. For the purpose of this TMDL, facilities permitted under 

the National Pollutant Discharge Elimination System (NPDES) Program are considered point sources. 

Similarly, for the purpose of this TMDL air sources of mercury identified in the Mercury Report to 

Congress (EPA, 1997) which are located in the watershed and within a 100-kilometer boundary around the 

watershed, referred to as the local airshed are treated as nonpoint sources. All other air sources, outside 

the local airshed, are considered background sources of mercury. The source assessment serves as the 

basis for development of a model, and as the basis for the allocation of the total allowable load. 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

27

6.2.1. Sources of Mercury

It is estimated that approximately 99% of the mercury loading to the watershed is from atmospheric 

deposition (See Table 8 Annual Average Total Mercury Load). Mercury is deposited to the watershed as 

wet deposition (dissolved in rain) and as dry deposition of gaseous and particulate forms of mercury. For a 

more inclusive discussion of the air analysis performed as part of this TMDL, see Appendix A. Mercury 

deposited in the watershed comes from sources within the local airshed, from national sources located 

beyond the local airshed, and from international sources far away. Reactive gaseous mercury (RGM) is the 

dominant form of mercury in both rainfall and most dry deposition processes, and most of the RGM emitted 

from man made sources is deposited relatively quickly. Therefore, the analysis of air point sources focuses 

on sources located in the local airshed, and on their emissions of RGM to the air. For the purposes of this 

TMDL, the sources within the local airshed are treated as the nonpoint sources of mercury. Those sources 

outside the local airshed are considered to be part of the background load of mercury since identification of 

the distant sources that contribute mercury to the watershed was not accomplished for this Phase 1 TMDL. 

 

The emissions inventory files prepared for the Mercury Report to Congress (EPA, 1997) identify stationary 

point sources of mercury in Georgia and South Carolina within the local airshed. Table 3 identifies these 

stationary sources of mercury deposition and their estimated contribution in 1995 of RGM, the form of 

mercury that is most likely to deposit within the local airshed, including the Savannah River watershed. 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

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Table 3 Summaries of Mercury Emissions in the RGM Airshed during the Baseline Period (1994-1996)

Source Category No. of 

Sources

Total Hg 

Emissions

Baseline 

Period

(kg/yr)

% of 

Total Hg

% of 

Total Hg 

that is 

RGM

Total RGM 

Emissions

Baseline

% of 

Total 

RGM

MedWIs 36 963 25.65 73 703 39.93

Power Plants 17 866 23.08 30 260 14.76

Chlor-alkali 1 597 15.92 30 179 10.18

MuniWCs 3 589 15.69 60 353 20.08

Res/Ind Boilers 80 477 12.70 30 143 8.12

Pulp and Paper 12 121 3.23 30 36 2.06

Portland Cement 3 113 3.01 10 70 3.95

Sew Sludge Incin 6 26 0.69 60 16 0.88

HazWIs 2 1 0.03 8-95 <1 0.02

Total 160 3753 100.00 1760 100.00

6.2.2. Water Point Sources

Facilities covered by the National Pollutant Discharge Elimination System (NPDES) program are 

considered in this TMDL to be point sources of mercury within the Savannah watershed. There are 

approximately 80 NPDES facilities in Georgia discharging effluent to the Savannah River and its tributaries. 

(See Appendix B for a list of these facilities.) Because of the pervasive nature of mercury, and its presence 

in rainwater, it is assumed that all NPDES facilities discharge some mercury to the River. Because, until 

recently, EPA’s published method for the analysis of mercury was not sensitive enough to measure mercury 

at low trace level concentrations, most NPDES facilities have not detected mercury during priority pollutant 

monitoring. Therefore, most facilities do not have permit limits for mercury in their NPDES permits since 

they have not demonstrated “reasonable potential” for mercury in their effluent. This TMDL will address 

only those facilities that have the potential to discharge mercury above 2.8 ng/l (the applicable water quality 

standard as interpreted by EPA) and that may be adding mercury to their effluent above that in their present 

source water (See Section 10.2).
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

29

In 1999, EPA published a new analytical detection method for mercury that can reliably measure the 

chemical down to 0.5 ng/l (64 CFR 30417). Using this more sensitive analytical procedure and related 

field sampling protocols, EPA sampled a small cross section of the NPDES facilities in Georgia in the 

watershed (22 out of approximately 80 facilities). This limited sampling study confirmed EPA’s suspicion 

that all NPDES facilities are discharging some concentration of mercury. Half of the facilities sampled (11 

out of 22) are discharging mercury at a concentration below the water quality standard as interpreted by 

EPA of 2.8 ng/l, and the other half are discharging above this concentration. Based on the limited data from 

this one-time sampling event, EPA is estimating that NPDES point sources contribute approximately 1% of 

the current total load of mercury to the River. 

6.3. RELMAP Mercury Deposition Rates

As part of the Mercury Report to Congress, a national airshed model (RELMAP) was applied to the 

continental United States. This model provides a distribution of both wet and dry deposition of mercury as 

function of air emissions and global sources. Figure 6 and Figure 7 illustrate the dry and wet deposition 

rates for the Savannah River watershed as derived by RELMAP. The RELMAP model was based upon 

the existing emissions inventory (1995 and 1996) and did not include some foreign airsheds (e.g., Mexico). 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

30

Figure 6 Mercury Dry Deposition Rates as Reported in the Mercury Report to Congress
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

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Figure 7 Mercury Wet Deposition Rates as Reported in the Mercury Report to Congress

6.4. Available Monitoring Data

The States of Georgia and South Carolina have routinely collected fish from the Savannah River for fish 

tissue analysis. Because mercury may bioaccumulate in fish tissue to mg/kg levels (parts per million), 

analytical procedures have been capable of detecting mercury at these levels. Therefore, data is available 

from the states for 1988 to 1998 on fish tissue from the Savannah River. These data indicate fish tissue, on 

average; exceed the State’s Fish Consumption Guidelines in the water segments covered by this TMDL. In 

addition, EPA conducted a field sampling study in August and September of 2000 that included fish-tissue 

sampling and analysis. These data are available below in Section 6.4.4.
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32

The states have also collected and analyzed ambient water concentration samples for total mercury. As 

explained above in Section 6.2.2, the analytical method for mercury used in the recent past has a detection 

limit of 200 ng/l, which is not sensitive enough to detect mercury at the low concentrations typically found in 

ambient surface water (rivers, creeks, and estuaries.) Therefore, laboratory results from samples of surface 

water collected by the states during their routine surface water monitoring programs typically have indicated 

a non-detect for mercury. Therefore, there is little ambient surface water mercury data available from the 

states. EPA’s sampling study of the listed segments of the Savannah River in August and September of 

2000 (EPA, November 2000) included water samples from 16 locations within the watershed. Samples 

were analyzed using EPA Method 1631, which has a detection limit of 0.5 ng/l. The results are presented 

below at Section 6.4.2. 

6.4.1. EPA Region 4 Data

EPA Region 4 sampled the Savannah River watershed in August and September of 2000. Since even low 

concentrations of mercury in water can lead to significant accumulation of mercury in fish tissue, EPA 

sampled the Savannah River using the most sensitive sampling and analytical techniques. The samples were 

collected using the “clean hands” method (EPA, November 2000), and analyzed using the ultra-trace level 

analytical technique, EPA Method 1631 (USEPA, 1999). EPA adopted this method in June of 1999 for 

mercury in water for data gathering and compliance monitoring under the Clean Water Act and Safe 

Drinking Water Act. This method can reliably measure mercury to 0.5 ng/l (parts per trillion).

The purpose of this data collection effort was to collect data needed for the development of this mercury 

TMDL. The sample locations for the water column are illustrated in Figure 8. Water column, sediment and 

soil samples (taken adjacent to the water column samples outside the flood plain) were taken from 10 

locations in the mainstem and 6 locations in tributaries throughout the middle and lower Savannah River 

watershed. 
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Figure 8 Savannah Watershed Water Column Sample Locations

Sample locations for the fish collection are illustrated in Figure 9. The 16 collection sites are located 

throughout the mainstem and tributaries in the middle and lower Savannah Basins. The fish collection 

consisted of 5 fish per sampling location, with the species of interest being largemouth bass. Largemouth 

bass were targeted because the State of Georgia’s Fish Consumption Guideline is established to protect 

consumers from the consumption of largemouth bass. When 5 largemouth bass were not obtainable, other 

fish (Bowfin, Chain Pickerel, Grass Pickerel) were substituted.
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

34

Figure 9 Savannah Watershed Fish Collection Locations

The following sections provide the results of the field sampling for mercury.

6.4.2. Water Column Data

Water column samples were taken to determine the ambient concentration of mercury in the water column 

using Method 1631, an ultra-trace level clean sampling and analytical technique with a quantification level of 

0.5 ng/l. The water column samples were analyzed for both total mercury and methylmercury. Because 

methylmercury is the primary form of mercury taken up in the food chain, it was important to quantify the 

fraction of the total mercury in the methyl form. Table 4 provides the measured mercury concentrations in 

the water column in mainstem and tributaries in the Middle/Lower Savannah watershed.
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

35

Table 4 Water Column Mercury Concentrations

ID Station Total 

Hg (ng/l)

MeHg 

(ng/l)

Percent 

MeHg

M-0 Savannah River-Below Clark's Hill Dam 0.27 0.02 7.8

M-1 Savannah River-Below Horse Creek 0.68 0.10 14.1

M-2 Savannah River-Below Butler Creek 1.19 0.16 13.1

M-3 Savannah River-Below Upper Three Runs Creek 3.27 0.07 2.0

M-4 Savannah River-Below Lower Three Runs Creek 9.50 0.06 0.6

M-4 Savannah River-Below Lower Three Runs Creek(Filtered) 1.47 0.07 4.4

M-5 Savannah River-Below Brier Creek 2.80 0.09 3.2

M-6 Savannah River-Clyo, USGS Gage 3.28 0.09 2.7

M-7 Savannah River-Below Ebenezer Creek 3.44 0.08 2.2

M-8a Savannah River-Tide Gate (Freshwater) 4.44 0.09 2.1

M-8a Savannah River-Tide Gate (Freshwater) (Filtered) 1.00 0.03 3.2

M-8b Savannah River-Tide Gate (Estuary) 4.09 0.06 1.5

T-1 Horse Creek 6.16 0.24 3.9

T-2 Butler Creek 2.14 0.39 18.2

T-3 Upper Three Runs Creek 5.82 0.16 2.7

T-4 Lower Three Runs Creek 2.43 0.13 5.1

T-5 Brier Creek 2.15 0.11 5.0

T-6 Ebenezer Creek 3.34 0.65 19.5

6.4.3. Sediment Data

Samples of river and tributary sediments were gathered at the same locations as the water samples to 

determine the amount of mercury associated with the sediments and porewater. This data provides 

important information that can be used to parameterize the water quality model by providing evidence of the 

effects of mercury in the sediments on the total mercury water column concentration.
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

36

Table 5 Sediment Mercury Concentrations

ID Station Total Hg 

(ng/g)

MeHg 

(ng/g)

Percent 

MeHg

M-0 Savannah River-Below Clark's Hill Dam 2.69 0.02 0.6

M-1 Savannah River-Below Horse Creek 10.16 0.00 0.0

M-2 Savannah River-Below Butler Creek 3.09 0.00 0.1

M-3 Savannah River-Below Upper Three Runs Creek 3.18 0.01 0.3

M-4 Savannah River-Below Lower Three Runs Creek 2.98 0.00 0.1

M-5 Savannah River-Below Brier Creek 10.08 0.01 0.1

M-6 Savannah River-Clyo, USGS Gage 2.53 0.12 4.7

M-7 Savannah River-Below Ebenezer Creek 83.36 0.56 0.7

T-1 Horse Creek 19.56 0.03 0.2

T-2 Butler Creek 14.02 0.02 0.1

T-3 Upper Three Runs Creek 3.08 0.00 0.1

T-4 Lower Three Runs Creek 3.13 0.00 0.1

T-5 Brier Creek 3.43 0.00 0.1

T-6 Ebenezer Creek 143.23 0.34 0.2

6.4.4. Watershed Soil Data

Soil samples were collected from the surrounding watershed where the other samples were taken. EPA 

collected the soil samples to be used in the calibration of the watershed model. Table 6 provides the 

mercury concentrations associated with soils collected during the summer of 2000.

Table 6 Mercury Concentrations in Soils from Surround Watershed

Station Percent 

Dry Wt.

Total Hg 

(ng/g) Dry 

 Weight

MeHg 

(ng/g) Dry 

Weight

Savannah River-Below Clark's Hill Dam 75.7 78.6 0.04

Savannah River-Below Butler Creek 79.1 33.1 0.03

Savannah River-Below Upper Three Runs Creek 82.5 22.7 0.05

Savannah River-Below Lower Three Runs Creek 82.9 56.8 0.00

Savannah River-Below Brier Creek 90.8 43.6 0.26

Savannah River-Clyo, USGS Gage 78.1 71.8 0.95

Savannah River-Below Ebenezer Creek 94.5 33.9 0.01

Butler Creek 97 43.8 0.06
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

37

Horse Creek 82.6 43.6 0.01

Upper Three Runs Creek 82.5 56.4 0.01

Lower Three Runs Creek 66.1 137.7 0.54

Brier Creek 84 26.3 0.32

Ebenezer Creek 91.7 28.1 0.11

6.4.5. Fish Tissue Data

Samples of fish were taken from the Savannah River and tributaries within the same area as the water 

column and sediment samples. Trophic level four fish (largemouth bass) were targeted in the collection 

because they represent a major portion of the fish size that is caught and kept by anglers and consumed as a 

source of food, and because Georgia’s Fish Consumption Guideline is based on the protection of public 

health from the consumption of largemouth bass. Trophic level four fish also represent the upper end of the 

food chain where the biomagnification of mercury would be the highest. The fish fillets obtained during 

EPA’s sampling effort were analyzed for total mercury. Table 7 provides the individual fish data. The fish 

tissue mercury concentration was used to determine the appropriate interpretation of Georgia’s water 

quality standard for use in the TMDL.

Table 7 Fish Tissue Mercury Data

Location Type

Total 

Length (mm) Wt. lbs.

Total Hg (Wet 

Weight) (mg/kg)

Below Clark's Hill Dam LMB 510 3.79 0.40

Below Clark's Hill Dam LMB 337 1.13 0.12

Below Clark's Hill Dam LMB 328 1.16 0.26

Below Clark's Hill Dam LMB 305 0.77 0.15

Below Clark's Hill Dam LMB 319 0.94 0.32

Horse Creek LMB 340 1.22 0.12

Horse Creek LMB 331 1.20 0.29

Horse Creek LMB 310 0.86 0.14

Horse Creek LMB 270 0.56 0.30

Horse Creek LMB 316 0.94 0.48

Below Horse Creek LMB 329 1.12 0.10

Below Horse Creek LMB 261 0.57 0.07
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

38

Location Type

Total 

Length (mm) Wt. lbs.

Total Hg (Wet 

Weight) (mg/kg)

Below Horse Creek LMB 255 0.47 0.08

Below Horse Creek LMB 218 0.33 0.05

Butler Creek GP 219 0.17 0.19

Butler Creek GP 170 0.08 0.45

Butler Creek GP 220 0.18 0.33

Butler Creek LMB 232 0.38 0.25

Below Butler Creek LMB 460 3.13 0.52

Below Butler Creek LMB 310 0.87 0.24

Below Butler Creek LMB 288 0.61 0.59

Below Butler Creek LMB 282 0.79 0.10

Below Butler Creek LMB 275 0.59 0.13

Upper Three Runs Creek Bowfin 585 4.21 1.04

Upper Three Runs Creek Bowfin 589 3.92 0.64

Upper Three Runs Creek Bowfin 567 3.72 0.54

Upper Three Runs Creek Bowfin 603 3.91 1.19

Upper Three Runs Creek Bowfin 505 2.67 0.50

Below Upper Three Runs Creek LMB 322 0.91 0.16

Below Upper Three Runs Creek LMB 340 1.03 0.22

Below Upper Three Runs Creek LMB 280 0.58 0.09

Below Upper Three Runs Creek LMB 304 0.78 0.28

Below Upper Three Runs Creek LMB 284 0.61 0.16

Lower Three Runs Creek Bowfin 624 5.12 1.36

Lower Three Runs Creek Bowfin 570 3.61 1.14

Lower Three Runs Creek Bowfin 509 2.45 0.76

Lower Three Runs Creek Bowfin 588 3.38 1.22

Lower Three Runs Creek Bowfin 540 3.01 0.95

Below Lower Three Runs Creek LMB 302 0.76 0.10

Below Lower Three Runs Creek LMB 401 1.90 0.34

Below Lower Three Runs Creek LMB 294 0.70 0.15

Below Lower Three Runs Creek LMB 355 1.41 0.22

Below Lower Three Runs Creek LMB 273 0.57 0.08

Brier Creek LMB 290 0.59 0.48

Brier Creek LMB 263 0.47 0.78
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

39

Location Type

Total 

Length (mm) Wt. lbs.

Total Hg (Wet 

Weight) (mg/kg)

Brier Creek LMB 255 0.47 0.71

Brier Creek LMB 235 0.37 0.23

Brier Creek LMB 214 0.25 0.27

Below Brier Creek LMB 302 0.76 1.04

Below Brier Creek LMB 401 1.90 0.33

Below Brier Creek LMB 294 0.70 0.34

Below Brier Creek LMB 355 1.41 0.14

Below Brier Creek LMB 273 0.57 0.23

Clyo, USGS Gage LMB 477 3.98 1.44

Clyo, USGS Gage LMB 301 0.83 0.36

Clyo, USGS Gage LMB 310 0.71 0.51

Clyo, USGS Gage LMB 295 0.65 0.50

Clyo, USGS Gage LMB 295 0.69 0.36

Ebenezer Creek Bowfin 654 2.32 1.02

Ebenezer Creek Bowfin 545 2.30 2.17

Ebenezer Creek Chain Pickerel 415 0.98 1.25

Ebenezer Creek Chain Pickerel 365 0.59 0.82

Ebenezer Creek LMB 285 0.64 1.08

Below Ebenezer Creek LMB 325 0.91 0.25

Below Ebenezer Creek LMB 272 0.56 0.41

Below Ebenezer Creek LMB 275 0.51 0.40

Below Ebenezer Creek LMB 465 3.00 1.07

Below Ebenezer Creek LMB 500 3.94 1.19

Tide Gate (Freshwater) Bowfin 570 3.96 0.19

Tide Gate (Freshwater) Bowfin 570 3.94 0.68

Tide Gate (Freshwater) Bowfin 572 3.94 0.97

Tide Gate (Freshwater) LMB 260 0.45 0.19

Tide Gate (Freshwater) LMB 280 0.61 0.21

Tide Gate (Freshwater) LMB 250 0.42 0.20

Tide Gate (Estuary) Striper 490 2.98 0.34

Tide Gate (Estuary) Striper 530 3.71 0.35

Tide Gate (Estuary) Striper 540 3.94 0.34

Tide Gate (Estuary) Striper 340 3.29 0.39
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

40

Location Type

Total 

Length (mm) Wt. lbs.

Total Hg (Wet 

Weight) (mg/kg)

Tide Gate (Estuary) Striper 505 3.10 0.54

7. Model Development

The link between the fish tissue residue concentration and the identified sources of mercury is the basis for 

the development of the TMDL. The linkage is defined as the cause and effect relationship between the 

selected indicators, the fish tissue residue concentration and identified sources. This provides the basis for 

estimating the total assimilative capacity of the river and any needed load reductions. In developing this 

TMDL, EPA combined models of watershed loading of mercury with a model of mercury cycling and 

bioaccumulation in the water. This enables a translation between the end-point for the TMDL (expressed 

as a fish tissue residue concentration of mercury) and the mercury loads to the water. The loading capacity 

of the River for mercury is then determined by the linkage analysis as a mercury-loading rate that is 

consistent with meeting the end-point fish tissue residue concentration.

7.1. Watershed Hydrologic and Sediment Loading Model

An analysis of watershed loading could be conducted at various levels of complexity, ranging from a 

simplistic gross estimate to a dynamic model that captures the detailed runoff from the watershed to the 

receiving waterbody. The limited amount of data available for the Savannah River watershed prevented 

EPA from using a detailed dynamic watershed runoff model, which needs a great deal of data for 

calibration. Instead, EPA determined the mercury contributions to the Savannah River from the surrounding 

watershed and atmospheric components based on an annual mass balance of mercury in water and 

sediment loading from the watershed. 

Watershed-scale loading of mercury in water and sediment was simulated using the Watershed
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

41

Characterization System (WCS) (USEPA, 2001). The complexity of this loading function model falls 

between that of a detailed simulation model, which attempts a mechanistic, time-dependent representation of 

pollutant load generation and transport, and simple export coefficient models, which do not represent 

temporal variability. The WCS provides a mechanistic, simplified simulation of precipitation-driven runoff 

and sediment delivery, yet is intended to be applicable without calibration. Solids load from runoff can then 

be used to estimate pollutant delivery to the receiving waterbody from the watershed. This estimate is 

based on mercury concentrations in wet and dry deposition, which is processed by soils in the watershed 

and ultimately delivered to the receiving waterbody by runoff, erosion and direct deposition (EPA, 

November 2000)

7.2. Water Quality Fate and Transport Model

Water Quality Analysis Simulation Program (WASP5) (Ambrose, et al., 1993) was chosen to simulate 

mercury fate in the Savannah River. WASP5 is a general dynamic mass balance framework for modeling 

contaminant fate and transport in surface waters. Based on the flexible compartment modeling approach, 

WASP can be applied in one, two, or three dimensions with advective and dispersive transport between 

discrete physical compartments, or segments. A body of water is represented in WASP as a series of 

discrete computational elements or segments. Environmental properties and chemical concentrations are 

modeled as spatially constant within segments. Each variable is advected and dispersed among water 

segments, and exchanged with surficial benthic segments by diffusive mixing. Sorbed or particulate fractions 

may settle through water column segments and deposit to or erode from surficial benthic segments. Within 

the bed, dissolved variables may migrate downward or upward through percolation and pore water 

diffusion. Sorbed variables may migrate downward or upward through net sedimentation or erosion. 

Two WASP models are provided with WASP5. The toxics WASP model, TOXI5, combines a kinetic 

structure adapted from EXAMS2 with the WASP5 transport structure and simple sediment balance 

algorithms to predict dissolved and sorbed chemical concentrations in the bed and overlying waters. 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

42

TOXI5 simulates the transport and transformation of one to three chemicals and one to three types of 

particulate material. The three chemicals may be independent, such as isomers of PCB, or they may be 

linked with reaction yields, such as a parent compound-daughter product sequence. Each chemical exists 

as a neutral compound and up to four ionic species. The neutral and ionic species can exist in five phases: 

dissolved, sorbed to dissolved organic carbon (DOC), and sorbed to each of the three types of solids. 

Local equilibrium is assumed so that the distribution of the chemical between each of the species and phases 

is defined by distribution or partition coefficients. The model, then, is composed of up to six systems, three 

chemical and three solids, for which the general WASP5 mass balance equation is solved.

The WASP model was parameterized to simulate the fate and transport of mercury for the development of 

this TMDL. Site specific and literature values were used to predict water column concentrations as a 

function of flow.

8. Total Maximum Daily Load (TMDL)

The TMDL is the total amount of a pollutant that can be assimilated by the receiving waterbody without 

exceeding the applicable water quality standard, in this case, a numeric interpretation of the State of 

Georgia’s narrative water quality standard for toxic substances of 2.8 nanograms per liter (ng/l). This 

TMDL determines the maximum load of total mercury that can enter the Savannah River watershed within a 

year without exceeding 2.8-ng/l total mercury in the water column. (See Section 5 for a discussion of EPA’s 

interpretation of Georgia’s water quality standard for this TMDL.)

8.1. Critical Condition Determination

The average annual flow and average annual loading represents the critical conditions for this TMDL. 

Average annual flow and average annual loading are appropriate for several reasons. First, EPA’s human 

health methodology, which has been used to derive an appropriate numeric interpretation of Georgia’s 

narrative water quality standard for toxic substances for this TMDL, assumes that health effects due to 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

43

mercury occur as a result of long-term exposure to mercury in fish tissue through consumption of 

contaminated fish. The bioaccumulation of methylmercury in fish tissue is a long-term, multi-year, process. 

In fact, the applicable water quality standard as interpreted by EPA in this TMDL is based upon a 

largemouth bass of 315 millimeters in length, which represents a 3 to 5 year old bass. Therefore, the annual 

average load is more appropriate than a daily load for representing the long-term processes of

bioaccumulation in fish tissue that are associated with the potential for health effects. Second, the State 

applies their human health criteria at a flow equivalent to the annual average flow (Georgia Rules and 

Regulations for Water Quality Control, Chapter 391-3-6-.03(5)(e)(iv) which requires the application of 

average annual load in the TMDL. 

8.2. Seasonal Variation

Mercury is expected to fluctuate based on the amount and distribution of rainfall, and variable emissions 

from local and distant atmospheric sources. Since wet deposition is greatest in the spring and winter 

seasons, loadings of mercury are highest during these seasons. However, these seasonal impacts or other 

short-term variability in loadings are damped out by the biotic response of bioaccumulation, which as 

discussed above, is a long-term process. Therefore, seasonal variations are not important in this TMDL, 

which is expressed as an average annual load.

Methylation of mercury is expected to be highest during the summer because high temperatures and static

hydrologic conditions result in hypoxic and/or conditions that promote methylation, and since predator 

feeding activity is also high during the summer, mercury bioaccumulation is expected to be greatest during 

the summer. However, based on the refractory nature of mercury, seasonal changes in body burden would 

be expected to be slight. Inherent variability of mercury concentrations between individual fish of the same 

and/or different size categories is expected to be greater than seasonal variability.
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

44

8.3. Margin of Safety

A Margin of Safety (MOS) is a required component of a TMDL that accounts for the uncertainty about the 

relationship between the pollutant loads and the quality of the receiving waterbody. The MOS is typically 

incorporated into the conservative assumptions used to develop the TMDL. A MOS is incorporated into 

this TMDL in a variety of ways. These include: 

• Selecting the highest predicted water column concentration of mercury in the entire stretch of river 

to determine the load reduction needed to achieve Georgia’s water quality standard. This approach 

conservatively assumes that fish are exposed to the highest water column concentration and 

accounts for uncertainties associated with identifying the precise locations where the fish take in 

mercury.

• Calculating BAFs from only trophic level four fish. This approach conservatively assumes that the 

public consumes only largemouth bass. This may be an over-estimate of amount of mercury to 

which the public is exposed through fish consumption because the typical diet of fish from other 

trophic levels that do not bioaccumulate mercury to the same degree as trophic level four fish. 

However, this assumption contributes to the TMDL’s margin of safety because it accounts for 

uncertainties associated with precise fish diet. It also protects members of the public that consume 

fish from different trophic levels, but at a rate higher than the 17.5 g/day fish consumption rate 

employed for this TMDL.

• Assigning a 1% load reduction to point sources. While EPA believes that such reductions, 

considered together with reductions from air sources, are necessary to achieve water quality 

standards, EPA also recognizes that future studies of mercury emissions from air sources may 

indicate that water quality standard can be achieved solely by controlling air sources. By assigning 

a 1% load reduction to point sources, EPA accounts for the possibility that air source reductions 

are insufficient. Thus, in addition to reflecting what EPA believes today are necessary load 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

45

reductions from point sources, the 1% reduction helps account for EPA’s lack of precise 

knowledge concerning the relationship between the effects of Clean Air Act controls and water 

quality.

• Incorporating a number of conservative assumptions in deriving the estimate of anticipated 

reductions in emissions to the air. These are described in the Analysis of Atmospheric Deposition 

of Mercury to the Savannah River Watershed (2000). In addition, the resulting estimate does not 

take into account reductions resulting from voluntary control measures or new regulations. 

Therefore, reductions from air sources may possible be greater than presently estimated.

9. TMDL Development

In order to establish the maximum annual average load of mercury that be assimilated by the Savannah River 

and achieve the appropriate water quality standard, interpreted by EPA to be 2.8 ng/l, the watershed 

loadings of mercury to the River must be integrated with the fate and transport of mercury in the River. As 

discussed above (Section 8.1.), annual average loads and average annual flows are used as the basis for 

assessing the current loadings of mercury to the River and to assess the future load reductions of mercury 

needed to achieve the applicable water quality standard.

9.1. Model Results

Both the Watershed Characterization System (WCS) nonpoint source runoff model and the receiving 

waterbody model (WASP5) are used to determine the maximum load of mercury that can occur and not 

exceed the applicable water quality standard of 2.8 ng/l as interpreted by EPA. This section provides 

detailed information on how the models are applied, how the watershed and waterbody are broken down 

into segments (computational boxes) and how the mercury is transported throughout the watershed. 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

46

9.1.1. Nonpoint Source 

The main driving force for the WCS mercury model is the input of the appropriate wet and dry deposition 

rates for mercury. The wet and dry deposition rates that were used in the WCS model were derived from 

the RELMAP air deposition model results reported in the Mercury Report to Congress. The RELMAP 

predictions for both wet and dry deposition were converted to a GIS coverage (Figure 6 and Figure 7) to 

provide a spatially variable deposition rate for the watershed. The WCS model was used to calculate the 

total load of mercury entering the mainstem portion of the Savannah River from the sub basins delineated in 

Figure 3. The predicted annual loads are given in Table 8. For each of the sub basins, the total load is 

presented in mg/yr, and the percentage of the contribution of mercury from soil/erosion, runoff, direct 

deposition and impervious soil are presented. The watershed model was calibrated to match the soil 

concentrations that were measured in the field. 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

47

Table 8 Annual Average Total Mercury Load

Sub Watershed

Area 

(ha)

Total Load 

mg/yr Load/ha

% Impr 

Soil

% 

Sediment

% 

Runoff

% Direct 

Dep

% 

NPDES

Kiokee 32836.2 1669435.968 17.84 11.77 65.95 13.57 8.71 0

Little Kiokee 10088.81331540.4058 11.05 31.17 23.49 34.63 10.7 0

Horse 42746.975147562.706 41.76 48.53 7.95 35.83 7.68 0

Butler 25390.8 3334875.266 49.68 66.84 7.04 14.13 11.98 0.01

Hollow 29416.432526441.021 29.43 37.81 33.08 22.42 6.69 0

Upper Three Runs 56241.643329200.071 22.57 58.61 11.55 27.76 2.09 0

Fourmile 8710.13 3595104.186 14.92 60.68 1.25 32.14 5.93 0

Lower Three Runs 46814.15363748.1273 19.34 34.16 23.6 34.85 19.89 0

Brier Creek, SC 6666.03 2997886.561 22.05 30.02 36.68 29.28 4.02 0

Watchcall 8565.4 440622.7377 19.56 22.18 38.29 34.33 5.19 0

Boggygut 12453.06513979.5685 15 17.29 47.96 25.32 9.42 0

Newberry 10942.14566475.2132 18.24 30.34 35.14 20.52 14 0

Steel 18310.91793120.762 12.03 42.15 1.43 45.59 37.34 0

Beaverdam 12445.57630715.4352 17.83 41.31 18.39 23.24 16.96 0.1

Sweetwater 15726.241025257.81 21.55 18.38 34.82 29.49 17.3 0

Rocky 17327.971190980.475 22.3 10.02 51.67 21.94 16.37 0

King 7684.87 483180.7 22.22 12.57 20.19 23.28 43.96 0

McDaniel 7389.59 369119.15 17.92 15.7 15.71 22.93 45.66 0

Dry 10533.89835142.4918 25.97 19.63 40.85 30.46 9.06 0

Buck 24444.061448923.275 20.02 16.76 35.24 26.26 21.73 0

Utchee 42722.193836027.353 33.56 57.18 9.71 12.67 20.42 0.02

Spirit 36322.281933472.456 19.07 43.43 18.67 21.09 16.39 0.68

McBean 28999.992996561.842 15.72 24.1 38.67 25.45 11.78 0

Boggy 18934.66993640.7169 17.21 21.83 30.71 40.29 7.17 0

Jackson 15552.96945151.025 20.75 17.3 35.21 21.92 25.57 0

Cypress 23982.3 942136.3707 13.05 22.65 32.07 33.37 11.91 0

Ebenezer 60100.2 1995424.682 11 21.56 24.35 38.82 15.26 0.01

Pipemaker 52092.533482463.854 25.96 32.44 2.04 8.72 56.39 1

Lockner 7001.55 209844.6119 10.33 42.03 11.97 38.36 6.88 0.75

Sand 22305.24618689.0742 9.54 33.85 17.55 34.7 13.9 1.53

Brier Creek, GA 219195.99230475.848 10.92 31.01 25.68 36.62 6.68 0
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

48

9.1.2. Water Quality Model

The WASP5 toxic chemical program TOXI5 was set up to simulate mercury in the mainstem of the 

Savannah River. The segments identified in Section 1 comprise the mainstem of the Savannah River for the 

purposes of this analysis. The mainstem of the river was divided into 31 reaches. Each reach was further 

divided into 2 vertical compartments representing surface water and surficial sediment. The 2 centimeters 

(cm) deep surficial sediment layer actively exchanges silt and clay-sized solids as well as chemicals within 

the water column. In addition, this layer is the site for active microbial transformation reactions. Sedimentwater column diffusion coefficients were set at 10-5

 cm2/sec. Two classes of solids, sand and silt, were 

simulated. Sand makes up most of the benthic sediment compartments, which have a dry bulk density of 

0.5 g/ml. Given a particle density of 2.7 g/ml, the sediment porosity is about 0.8 and the bulk density is 1.3 

g/ml. Silt is found both suspended in the water column and in the sediment. These simulations assumed that 

10 mg/L of silt enters the mainstem from the subwatersheds, settling out at an assumed velocity of 0.3 

m/day. Silt in the surficial sediment compartments is assumed to resuspend at a velocity of 0.006 m/day, 

giving a concentration of about 0.005 g/ml, or about 1% of the surficial sediment. The exchanging silt 

carries sorbed mercury between the water column and surficial sediment. Mercury was simulated as 3 

components B elemental mercury, Hg0; inorganic divalent mercury, Hg(II); and monomethyl mercury, 

MeHg. Hg(II) and MeHg partition to solids and dissolved organic carbon (DOC). These are represented 

as equilibrium reactions governed by specified partition coefficients. The three mercury components are

also subject to several transformation reactions, including oxidation of Hg0 in the water column, reduction 

and methylation of Hg(II) in the water column and sediment layer, and demethylation of MeHg in the water 

column and sediment layer. These are represented as first-order reactions governed by specified rate 

constants. Reduction and demethylation are driven by sunlight, and the specified surface rate constants are 

averaged through the water column assuming a light extinction coefficient (here, 0.5 m-1). In addition to 

these transformations, Hg0 is subject to volatile loss from the water column. This reaction is governed by a 

transfer rate calculated from velocity and depth, and by Henry’s Law constant, which was set to 7.1 H 10-3
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

49

L-atm/mole-K. Under average flow conditions, velocity ranges from 0.2 to 0.3 m/sec, while depth ranges 

from 0.37 to 0.69 m. The specified and calculated reaction coefficients used here are summarized in Table 

9.

Table 9 Specified and Calculated Reaction Rates and Coefficients

Component Reaction Compartment Coefficient Value

Volatilization Water 1.0 - 3.9 day-1 (calc)

Hg0 Oxidation Water 0.0001 day-1

Reduction Water 0.010 day-1 (surface)

0.074 - 0.090 (calc)

Methylation Water 0.0001 day-1

Methylation Sediment 0.00002 day-1

Partitioning to silt Water, Sediment 4 x 105 L/kg

Partitioning to sand Water, Sediment 1 x 104 L/kg

Hg(II)

Partitioning to DOC Water, Sediment 2 x 104 L/kg

Demethylation to Hg(II) Water

Sediment

0.0001 day-1

0.00002 day-1

Demethylation to Hg0 Water (Photolysis) 0.1 day-1 (surface)

0.074 - 0.090 (calc)

Partitioning to silt Water, Sediment 4 x 105 L/kg

Partitioning to sand Water, Sediment 1 x 103 L/kg

MeHg

Partitioning to DOC Water, Sediment 2 x 105 L/kg

Two separate simulations of mercury in the Savannah River were run representing average flow and drought 

flow conditions. The average flow simulation was run for 30 years, so that steady-state conditions are 

achieved in the water and surficial sediment. Drought flow conditions were run for 180 days using the 

average-flow concentrations as initial conditions. Volumes, depths, and velocities were obtained from the 

EPDRIV1 hydrodynamic model currently being applied to Savannah River in support of work being 

conducted by Georgia EPD.

The flows, depths, velocities, and volumes used for average and drought conditions are summarized in Table 

10.
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

50

Table 10 Flows, Depths, Velocities and Volumes used in WASP Model

River Mile Segment Volume (m) Depth (m) Velocity (m/sec) Tributary Flow (cms)

213 1 2916469 2.33 0.43 Headwater 273.49

203 2 2427977.4 2.52 0.53

197 3 3737187.3 3.50 0.68

193 4 5808927.7 6.96 0.27

190 5 6741527 7.53 0.28 Horse Creek 4.50

186 6 4740424.8 7.44 0.38

182 7 3374938.1 7.20 0.37

179 8 2684006.2 5.87 0.61 Butler Creek 0.85

175 9 4041461.1 6.20 0.69 Spirit Creek/Bear 

Island

2.15

169 10 3085140.2 5.74 0.75 Hollow Creek 2.41

164 11 3806153.5 6.98 0.65 0.00

159 12 3738075.5 5.84 0.65 McBean, Boggy 

Gut, Newberry

2.83

154 13 2841953.7 6.71 0.66 Upper Three Runs 3.77

150 14 5921744 5.79 0.66 Fourmile Creek 1.10

142 15 7914561.9 5.70 0.65 Beaverdam, Steel 

Creek

3.34

133 16 9761070 5.57 0.81 Sweetwater, Lower 

Three Runs

3.99

116 17 6340925.8 5.63 0.70 Brier Creek, SC 1.81

107 18 7804913.5 5.96 0.65 Savannah Watch 

Call

2.04

96 19 5184161.4 6.95 0.72 Brier Creek, GA 25.57

89 20 3849710.4 7.51 0.67 0.00

84 21 3905226.2 7.21 0.70 Savannah Dry 

Branch

4.90

79 22 3989054.6 7.20 0.67 0.00

74 23 4086191.3 7.03 0.66 0.00

69 24 3918680.3 7.15 0.73 Boggy Branch 4.39

64 25 4858331.9 7.56 0.61 0.00

59 26 4767405.5 7.70 0.61 0.00

54 27 5109182.5 7.85 0.56 0.00

49 28 4910985.4 7.94 0.55 0.00

44 29 3656800.3 7.84 0.76 Ebenzer, Lockners, 

Abercorn

12.46

39 30 8558710.5 6.36 0.94 0.00

29 31 10107590 5.73 1.45 0.00

The WCS model calculates mercury loadings to each reach. These values are specified as constant Hg(II) 

and MeHg loadings for each surface water compartment. Loadings for average flow conditions reflect both 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

51

wet and dry deposition throughout the watershed, followed by runoff and erosion to the tributary stream 

network. Loadings for drought flow conditions include only dry deposition (11 ìg/m2-yr) directly to water 

surfaces. These loadings to the tributary network are subject to reduction and volatilization losses in 

transport to the mainstem. Under drought flow conditions, these losses could be very significant due to the 

long travel times. Average reduction factors were calculated for each tributary inflow using a reduction rate 

constant of 0.1 day-1 along with that subwatershed’s flow, water surface area, and assumed depth:

reduction factor=(1 - e ) / kr T

- k r T

max

max •

•

where kr is the reduction rate constant in day-1 and Tmax is the travel time for the tributary in days. The travel 

time is calculated as the total tributary surface area times its average depth divided by its average flow. 

Figure 10 compares the model predictions versus what was measured in the field summer of 2000. 

Because of the severe drought condition in Georgia prior to and during the sample collection, the only 

loading source of mercury to the watershed was direct deposition on the water. This modeling exercise was 

done to aid in the parameterization and calibration of the water quality model.
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

52

Low Flow Water Column Total Mercury Concentrations

0

1

2

3

4

5

6

7

8

9

10

250 200 150 100 50 0

River Mile

ng/lTotal Hg

Measured

Figure 10 Model Predictions versus Observed Data for the Savannah River for Drought Conditions

Figure 11 provides a comparison of model predicted mercury sediment concentrations versus what was 

measured in the field. 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

53

Low Flow Total Mercury Concentration in Sediments

0

5

10

15

20

25

30

250 200 150 100 50 0

River Mile

ug/kg

Predicted

Observed

Trib sediments

Figure 11 Model Predictions versus Observed Data for Total Mercury in the Sediments during Low Flow

Figure 12 provides the predicted water column concentrations under annual average load and flow for the 

Savannah River. The highest predicted water column concentration is used in the TMDL calculation to 

determine the maximum annual average load that could occur and still achieve the applicable water quality 

standard as interpreted by EPA. 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

54

Average Annual Flow Water Column Total Mercury Concentrations

0

1

2

3

4

5

6

7

8

9

10

250 200 150 100 50 0

River Mile

ng/l

Total Hg

Observed

Figure 12 Model Predictions versus Observed Data for the Savannah River for Annual Average Flow

Figure 13 provides a comparison of model predicted mercury sediment concentrations versus what was 

measured in the field under annual average flow conditions.
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

55

Total Mercury Concentration in Sediments Annual Average Flow

0

2

4

6

8

10

12

14

250 200 150 100 50 0

River Mile

ug/kg

Predicted

Observed

Figure 13 Model Predictions versus Observed Data for Total Mercury in the Sediments Annual Average Flow

9.2. TMDL Determination

To determine the total maximum load that can come into the Savannah River without exceeding the 

applicable water quality standard of 2.8 ng/l as interpreted by EPA, the current loading conditions are 

evaluated and the water column concentration in the River is determined using the modeling approach 

described above. This allows the development of a relationship between mercury loading and water column 

mercury concentrations in the River. Using this developed relationship, the total maximum load can be 

determined. Because the water column mercury concentration response is linear with respect to changes in 

load, a proportion can be developed to calculate the total maximum mercury load from the watershed that 

would achieve the derived water quality standard of 2.8 ng/l as interpreted by EPA. The TMDL is 

calculated as given below:
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

56

TMDL Load

WQS

Current Annual Average Load

Highest Segment Concentration

.

.

where:

Highest Segment Concentration = 5.0 ng/l

Current Annual Average Load to the Savannah River = 58.8 kilograms/year

Water Quality Standard = 2.8 ng/l as interpreted by EPA

The TMDL Load is calculated as 32.8 kilograms/year total mercury.

10. Allocation of Loads

In a TMDL assessment, the total allowable load is divided and allocated to the various pollutant sources. 

This allocation is provided as a Load Allocation (LA) to the nonpoint sources, defined in this TMDL as the 

air sources within the 100-kilometer boundary of the watershed, and as a Wasteload Allocation (WLA) to 

the point-source facilities in Georgia with a NPDES permit. The difference between the current load and 

the allowable load is the amount of pollutant reduction the sources need to achieve in order for the 

waterbody to ultimately achieve the applicable water quality standard of 2.8 ng/l as interpreted by EPA.

The calculated allowable load of mercury that can come into the Savannah River without 

exceeding the applicable water quality standard of 2.8 ng/l as interpreted by EPA is 32.8 

kilograms/year. Because this assessment indicates that 99% of the loading of mercury is from atmospheric 

sources, 99% of the allowable load will be assigned to the load allocation, and 1% of the available load will 

be assigned to the wasteload allocation. Therefore, the Load Allocation and Wasteload Allocation for the 

middle/lower Savannah River are:

Load Allocation (atmospheric sources) = 0.99 (32.8) = 32.5 kilograms/year

Wasteload Allocation (NPDES sources) = 0.01 (32.8) = 0.3 kilograms/year
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

57

The estimated current loading of mercury to the Savannah River from the surrounding watershed is 58.8 

kilograms/year. This load was determined by adding the predicted mercury load for each of the 

subwatersheds taking into account delivery times and volatilization that occurs in the tributaries. The 

difference between the estimated current mercury load (58.8 kg/year) and the calculated allowable load 

(32.8 kg/year) is 26 kilograms/year. Since 32.8 kg/year is 56% of the estimated current loading of 

mercury, it is estimated that a 44% reduction in total mercury loading is needed for the middle/lower 

Savannah River to achieve a water column concentration of 2.8 ng/l. 

10.1. Atmospheric Reductions

EPA estimates that approximately 99% of current mercury loadings to the River are from atmospheric 

deposition; therefore, significant reductions in atmospheric deposition will be necessary if the applicable 

water quality standard as interpreted by EPA of 2.8 ng/l is to be attained. Based on the total allowable load 

of 32.8 kilograms per year, a 44% reduction of mercury loading is needed to achieve the applicable water 

quality standard as interpreted by EPA. An analysis conducted by the EPA Region 4 Air Program 

(Appendix A) concludes that an estimated 38% to 48% reduction in mercury deposition to the Savannah 

River watershed can be achieved by 2010. This conclusion was derived using the following methodology:

• The analysis used the results of national atmospheric mercury deposition modeling done for EPA’s 

1997 Mercury Study Report to Congress (referred to as The Mercury Study) to estimate the 

level of mercury deposited to the Savannah River watershed during the baseline period (1994-

1996) from local sources (those in the watershed or within 100 km of the watershed), plus national 

and global sources. The analysis presumes that local sources primarily contribute to the loading by 

deposition of reactive gaseous mercury (RGM, divalent mercury gas), while national sources (i.e., 

at a distance >100 km) contribute particle bound mercury, and global sources contribute gaseous 

elemental mercury.

• The total RGM emitted from local sources was estimated for the baseline period from the emissions 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

58

data files used to conduct The Mercury Study modeling. Local sources include categories such as 

hospital and medical waste incinerators, municipal waste incinerators, electric utility plants, a chloralkali chlorine production facility, and industrial and residential boilers.

• Future RGM emissions for 2010 from local sources were estimated using projected population 

growth as an indicator of growth in emissions over time, along with calculated reductions in mercury 

emissions due to MACT and Waste Combustion controls. Then an estimate of RGM deposition to 

the watershed was calculated for 2010 as proportional to local emissions.

• Combining the RGM value with an estimate of proportional national and global source contributions 

in 2010 developed the sum total deposition of mercury to the watershed in 2010. Comparison of 

the total value emitted in 1995/1996 with the total value calculated for emissions in 2010 indicates 

that a 38% to 48% reduction of mercury deposition is probable over the approximately 15 years 

from the baseline to 2010, based on currently promulgated standards in the Clean Air Act (MACT 

and Section 129.)

EPA expects these reductions to be achieved through full implementation of currently promulgated Clean 

Air Act (CAA) requirements under Section 112(d) Maximum Achievable Control Technology (MACT) 

and Section 129 Solid Waste Combustion, and Section 111 New Stationary Sources, at sources within the 

local airshed and nationally. The local airshed is defined in this TMDL to be the area within the watershed 

and a 100-kilometer boundary around the watershed. Additional reductions may be realized after further 

implementation of these requirements and other Clean Air Act sections.

The analysis conducted by the EPA Region 4 Air Program in Appendix A provides reasonable assurance 

that reductions needed in mercury loading can be achieved by reductions in mercury emissions from air 

sources within the local airshed and nationwide. There are, however, uncertainties in the air deposition 

analysis that should be recognized and are explained in Appendix A. Some of these uncertainties include 

the estimates of the amount of the chemical form or species of mercury emitted by each source category; the 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

59

projected level of reductions from each source category subject to Section 129 or MACT regulations; the 

definition of local sources contributing deposition to the watershed, the contribution from global sources, 

and other aspects of the modeling. While it is not possible to quantify the net effect of these factors, EPA 

believes the assumptions made to address these uncertainties are reasonable and consistent with the stateof-the art mercury modeling available at the time this TMDL was prepared, and that the Agency has 

reasonable assurance that needed air reductions will be achieved notwithstanding these uncertainties. It is 

anticipated, however, that additional data and information collected during implementation of this Phase 1 

TMDL will allow a more certain analysis of attainable air reductions to be accomplished in the Phase 2 

TMDL. EPA will determine at that time whether it is appropriate to revise the load allocation, or the 

wasteload allocation, to assure that the applicable water quality standard as interpreted by EPA will be 

achieved.

Future additional reductions in air deposition of mercury, beyond that presented in Appendix A, may occur 

through the implementation of voluntary programs as well as new CAA regulatory actions being considered 

by EPA. This TMDL does not currently depend on any additional future reductions beyond those identified 

in Appendix A. While it is not possible at this time to quantify these anticipated mercury reductions, an 

estimate of such quantification will be more likely during the Phase 2 TMDL. In December 2000, EPA 

announced that it intends to begin developing a regulation under CAA Section 112 to limit mercury 

emissions from coal-fired power plants. A proposal is expected in late 2003 and a final regulation at the 

end of 2004. As a group, these plants are the largest remaining source of mercury emissions in the United 

States. It is too early to estimate the reductions in mercury emissions that may result from regulation of 

electric utilities. In the meantime, we expect to see reduced emissions of mercury from this sector as a 

number of regulations are implemented to control SO2 and NOx, since some control technologies used to 

limit these pollutants collaterally reduce mercury emissions as well. A review of regulatory and related 

initiatives to reduce mercury emissions is provided in Appendix A. At this time, the overall, or relative 

percent, reduction in mercury emissions that may be realized in the future from the variety of activities 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

60

underway or proposed is uncertain, and estimating such reductions is not appropriate for this TMDL. 

However, EPA is committed to continuing to track emissions of mercury and evaluate additional ways to 

reduce releases of mercury to the environment.

10.2. Allocation to NPDES Point Sources

This TMDL estimates that approximately 1% of the current loadings of mercury to the River are from 

NPDES point sources. For a discussion of EPA’s basis for this estimate, see Section 8.2.2. At this time, 

one NPDES point source in Georgia has a permit to discharge mercury to the Savannah River. This facility 

is the Olin Corporation located in Augusta (NPDES Permit Number GA0003719). The TMDL also 

identifies 28 other NPDES point sources in Georgia for a wasteload allocation in this TMDL that Georgia 

and EPA believe have the potential to discharge significant amounts of mercury in their effluent. Twentyfour of these facilities have been identified because of their volume of flow (greater than 1 million gallons per 

day) or based on limited effluent data or the fact that they were rated as “major industrial” facilities by the 

State of Georgia. In making such “major industrial” facility determinations, Georgia takes into account 

factors such as toxic pollutant potential, public health impacts, and impacts on water quality. Another 4 

facilities, considered to be “minor municipal” or “minor industrial” facilities, are also identified in the TMDL 

for a wasteload allocation. Data collected by EPA at these facilities in August 2000, indicate mercury 

concentrations in the facility’s effluent above the applicable water quality standard as interpreted by EPA of 

2.8 ng/l. EPA believes it is reasonable to assume that mercury is present in the discharge of these 29 

NPDES permittees because of the persistent nature of mercury, and its pervasive presence in the 

environment, including rainwater. Table 11 (below) provides the list of NPDES facilities in Georgia that are 

provided a wasteload allocation in this TMDL.

There are approximately 50 other NPDES permitted facilities in Georgia located within the watershed. 

(See Appendix B for a list of all NPDES facilities in the watershed of the middle and lower Savannah River 

Basin provided to EPA by the Georgia Environmental Protection Division.) The TMDL does not provide a 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

61

specific wasteload allocation to these facilities since they discharge less than 1 million gallons per day, or are 

considered “minor industrial” facilities. EPA assumes that these facilities are discharging mercury in 

concentrations below the 2.8-ng/l applicable water quality standard as interpreted by EPA, or are not 

adding concentrations of mercury above that in their source water. These facilities have a smaller flow rate 

(compared to the facilities identified above), and they are considered by the State of Georgia to be “minor 

municipal” or “minor industrial” facilities based on the factors set forth above (a “minor municipal” facility 

has flow less than 1 million gallons pre day). As the new more sensitive EPA Method 1631 mercury 

analytical procedure is implemented in the NPDES program these “minor” facilities must verify through 

monitoring whether or not they are significant contributors of mercury (State of Georgia Rules and 

Regulations for Water Quality Control, April 2000, Chapter 391-3-6-.06, and January 1995 Reasonable 

Potential Procedures). EPA can consider this information in the revision of the TMDL in 2004, and will 

establish a wasteload allocation for any facilities for which data demonstrates mercury is present in their 

effluent at levels above the amount present in their source water.

In order to achieve the water quality standard as interpreted by EPA for mercury in the Savannah River, 

EPA has assigned to all NPDES point sources in the basin a cumulative wasteload allocation of 0.3 kg/year. 

 For each of the 29 facilities identified as potential significant contributors of mercury, EPA is providing a 

specific wasteload allocation (WLA). This WLA is expressed in two different forms. The first is described 

as Option A below, and the second is described as Option B. The NPDES permitting authority is 

authorized by this TMDL to apply either option to the NPDES point sources affected by this TMDL. In the 

context of this TMDL, EPA believes it is reasonable to offer this choice to the permitting authority for the 

following reasons. First, based on EPA’s analysis, either wasteload allocation option, in the aggregate, is 

expected to result in point source mercury loadings less than the cumulative wasteload allocation. Second, 

EPA believes this flexibility is the best way of ensuring that the necessary load reductions are achieved 

without causing significant social and economic disruption. EPA recognizes that NPDES point sources 

contribute only a small share of the total mercury contributions to the Savannah River. However, EPA also 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

62

recognizes that mercury is a highly dangerous pollutant that can bioaccumulate in fish tissue at levels harmful 

to human health. Therefore, EPA has determined, as a matter of policy, that NDPES point sources known 

to discharge mercury at levels above the amount present in their source water should reduce their loadings 

of mercury using appropriate, cost-effective mercury minimization measure in order to ensure that the total 

point source discharges are at a level equal to or less than the cumulative wasteload allocation specified in 

this TMDL. The point sources’ WLA will be applied to the increment of mercury in their discharge that is 

above the amount of mercury in their source water. For further discussion of the legal and policy rationale 

underlying these wasteload allocations, see the Response to Comments. EPA recommends that the 

permitting authority make this choice between Option A and Option B in consultation with the affected 

discharger because EPA is not able to make the case-by-case judgments in this TMDL that EPA believes 

are appropriate. 

Option A: Criteria end-of-pipe

Under Option A, the wasteload allocation is equivalent to applying Georgia’s water quality standard as 

interpreted by EPA to the discharger’s effluent at the outfall point. For this TMDL, EPA has interpreted 

Georgia’s water quality standard to be 2.8 ng/l. Therefore, under this option, the wasteload allocation for 

each NPDES point source identified in this TMDL would be the product of multiplying 2.8 ng/l by the 

permitted or design flow rate of each identified NPDES point source. The result would be the maximum 

mass loading of mercury from that point source. The sum of these individual wasteload allocations is 0.001 

kg/year, which is significantly less than the 0.3 kg/year cumulative wasteload allocation provided to all 

NPDES facilities. Under Option A, the individual wasteload allocations for each NPDES point source 

affected by this TMDL are provided in Table 11.

Table 11 NPDES Permitted Facilities and Assigned Wasteload Allocation at 2.8 ng/l

Major Municipal NPDES ID MGD Kg/Yr

Augusta – Butler Creek GA0037621 46.1 1.78E-04

Columbia County – Crawford Creek GA0031984 1.5 5.81E-06

Columbia County – Reed Creek GA0031992 4.6 1.78E-05
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

63

Columbia County – Little River GA0047775 1.5 5.81E-06

Garden City WPCP GA0031038 2 7.74E-06

Richmond County – Spirit Creek GA0047147 2.24 8.67E-06

Savannah Crossroads (proposed facility) GA0038326 1.2 4.64E-06

Savannah - President Street GA0025348 27 1.04E-04

Savannah -Wilshire/Windsor GA0020443 4.5 1.74E-05

Savannah Travis Field GA0020427 1 3.87E-06

Sylvania WPCP GA0021385 1 3.87E-06

Tybee Island GA0020061 1 3.87E-06

Waynesboro GA0020231 2 7.74E-06

Major Industrial/Federal

DSM Chemicals Augusta Inc GA0002160 3.765 1.46E-05

Fort James GA0046973 18 6.97E-05

Georgia Power Vogtle GA0026786 7.2 2.79E-05

International Paper Company GA0002801 58.6 2.27E-04

Kemira GA0003646 23 8.90E-05

PCS Nitrogen Fertilizer L.P. GA0002071 1.152 4.46E-06

PCS Nitrogen Fertilizer LP GA0002356 0.362 1.40E-06

Savannah Electric Effingham GA0003883 108 4.18E-04

Stone Container GA0002798 4.86 1.88E-05

Union Camp Corporation GA0001988 28.09 1.09E-04

USA Fort Gordon GA0003484 1.921 7.43E-06

USA Hunter AFB STP GA0027588 0.544 2.11E-06

Significant Municipal Minors

DHR Gracewood School Rec WPCP GA0047279 0.5 1.94E-06

DHR Gracewood Hospital GA0022161 0.003 1.16E-08

Significant Industrial Minors

Olin Corporation Augusta GA0003719 1.246 4.82E-06

Citgo Asphault GA0004332 0.054 2.09E-07

 Option B: Mercury characterization or minimization

Under Option B, the individual wasteload allocations are equivalent to the level of mercury in a point 

source’s effluent after implementation, when appropriate, of cost-effective and appropriate mercury 

minimization measures. EPA assumes that feasible/achievable mercury load reductions resulting from the 

mercury minimization efforts will, as a cumulative amount of all 29 facilities, result in a total loading of less 

than 0.3 kg/year. This assumption is based on information indicating wastewater treatment plants, which

account for about 50% of the affected facilities, can attain significant mercury reductions through source 

reduction efforts. The effectiveness of mercury minimization efforts at industrial facilities is highly facilityspecific; however, significant reductions may be attained through product substitution and other measures 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

64

(See Mercury Report to Congress, 1997, Section 4, and Overview of Pollution Prevention Approaches at 

POTW’s, EPA 1999). If the cumulative effects of mercury minimization planning efforts are shown during 

the Phase 2 TMDL evaluation in 2004 not to be less than the cumulative 0.3 kg/yr wasteload allocation, 

EPA will provide a specific wasteload allocation to each facility to assure that the cumulative wasteload 

allocation will be attained.

Option B has a variety of different components that apply depending on whether the point source currently 

has a water quality-based effluent limitation for mercury in its NPDES permit. Affected NPDES permits 

would need to incorporate permit conditions or limitations as follows in order to be consistent with the 

assumptions of this TMDL. See 40 C.F.R. § 122.44(d)(1)(vii)(B).

For the NPDES facility in Georgia with a current permit limit for mercury (Olin Corporation, NPDES 

Permit Number GA0003719), this TMDL assumes that the permit will include:

• a numeric water quality-based effluent limitation for mercury that is identical to its current water 

quality-based limit for mercury;

• a requirement to monitor for mercury using the version of EPA Method 1631 then in effect;

• a requirement to expeditiously develop a mercury minimization plan; 

• a requirement to implement appropriate cost-effective mercury minimization measures identified 

through mercury minimization planning; and

• following completion of the mercury minimization plan, a numeric effluent limitation for mercury will 

be established in the permit that reflects the achievable level of mercury in the discharger’s effluent 

upon implementation of appropriate, cost-effective minimization measures.

For NPDES facilities in Georgia identified in Table 11 (except for Olin Corporation, NPDES Permit 

Number GA0003719) this TMDL assumes that the permits will includes: 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

65

• a requirement to characterize the effluent using the version of EPA Method 1631 then in effect in 

order to quantify the amount of mercury present in the influent and effluent, if any;

• a requirement to develop a mercury minimization plan if the monitoring data shows mercury is 

present in their effluent at levels greater than in their influent or source water, and the effluent 

concentration exceeds 2.8 ng/l). 

• a requirement to implement appropriate cost-effective mercury minimization measures identified 

through mercury minimization planning if the monitoring data shows that an increased amount of 

mercury is present in the final effluent (as described above).

While this TMDL assumes that the State of Georgia, as the permitting authority, will determine the 

necessary elements of a mercury characterization/ minimization study plan, EPA would expect the plan(s) to 

have elements similar to the following: (1) influent/effluent monitoring with sufficient frequency to determine 

variability and to identify if an increased amount of mercury is present. If the facility’s discharge is shown to 

result in an increased amount of mercury, the plan should also include the following additional elements: (2) 

the identification and evaluation of current and potential mercury sources; (3) monitoring to confirm 

current/potential sources of mercury; (3) the identification of potential methods for reducing/eliminating 

mercury, including housekeeping practices, material substitution, process modifications, materials recovery, 

spill control & collection, waste recycling, pretreatment, public education, laboratory practices, and disposal 

practices, and the evaluation of the feasibility of implementation; (4) implementation of cost-effective and 

appropriate minimization measures identified in the plan; and (5) monitoring to verify the results of waste 

minimization efforts. In addition, EPA expects the permit to establish a reasonable schedule for the 

implementation of each element and to require appropriate progress reports.

This TMDL accords the permitting authority a certain amount of discretion in incorporating these wasteload 

allocations into NPDES permits. The permitting authority is free to determine the appropriate frequency, 

duration and location of monitoring associated with the mercury characterization component of the 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

66

wasteload allocation. The permitting authority also has the discretion to determine the level of oversight in 

connection with the development of mercury minimization plans and the discharger’s choice of appropriate, 

cost-effective measures to implement. EPA believes that each of these decisions is heavily fact-dependant 

and that the permitting authority is in a better position than EPA to make them. 

As discussed below, this TMDL assumes that point sources will not be authorized to discharge mercury 

above current effluent levels. Option B is predicated on the judgment that the 0.3 mg/year cumulative 

wasteload allocation will be achieved by applying waste minimization measures to current point source 

effluent conditions. Allowing an increase in current effluent loadings of mercury could undercut the 

assumptions upon which this TMDL is based unless the permitting authority can demonstrate that any such 

increase is offset by decreases of mercury from other point source(s) so that the cumulative wasteload 

allocation of 0.3 kg/year is not exceeded.

EPA recognizes that the State of Georgia's regulations authorize compliance schedules for water qualitybased effluent limitations and conditions once those requirements are imposed in NPDES permits. See

Rules and Regulations for Water Quality Control, Chapter 391-3-6-.06(10). Under these regulations, the 

Director of EPD is authorized to establish as a compliance deadline the date that he or she determines to be 

“the shortest reasonable period of time necessary to achieve such compliance, but in no case later that an 

applicable statutory deadline.” Because there is no applicable statutory deadline relating to the achievement 

of these WLA-based limitations, point sources affected by this TMDL may be eligible for compliance 

schedules under this provision of Georgia's regulations. This TMDL assumes that the permitting authority 

will establish the shortest reasonable period of time for compliance with permit limitations and conditions 

based on this TMDL. This TMDL also recognizes, however, that the permitting authority is in the best 

position to determine the timing of mercury characterization and the compliance schedules for developing 

and implementing mercury minimization plans. 

Regarding the compliance schedules in permits to meet permit limitations and conditions based on Option B, 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

67

EPA makes the following observations. First, EPA believes that a point source with a flow of under 5 

million gallons per day can develop a detailed mercury minimization plan within three to six months after the 

mercury characterization phase is completed and it has been determined that a minimization plan is requires. 

 Point sources with a larger flow could develop a plan within about six to 12 months. Second, prompt 

characterization of the point sources’ mercury discharges will assist EPA in determining whether it is 

necessary to revise the TMDL in the near future. Any unnecessary delay in obtaining this information could 

interfere with that effort. Third, with respect to implementation of appropriate, cost-effective mercury 

minimization measures, EPA believes that the permitting authority is in the best position to determine what 

constitutes “the shortest reasonable period of time for compliance.” EPA recognizes that the

implementation of mercury minimization measures can take several years, especially when they involve small, 

diffuse sources discharging mercury to Publicly Owned Treatment Works (POTWs).

Other Assumptions Incorporated into this TMDL.

The wasteload allocation component of this TMDL reflects the following additional assumptions:

• The permitting authority may write permit conditions that allow the discharge of mercury at levels 

equal to the amount of mercury in the facility’s intake water (from the Savannah River or its 

tributaries), stormwater, and/or water drawn from the public water supply. If the permitting 

authority determines that mercury is present in the final effluent at levels above that level present in 

the influent, the permitting authority will establish permit limits consistent either Option A or Option 

B of this WLA. The permitting authority also should consider whether any increased mercury 

concentration in such discharges present potential for violation of an applicable acute standard for 

mercury, and include appropriate limits to protect against such violations. 

• No NPDES point source will be authorized to increase its mass loadings of mercury above levels 

reflected in current water quality-based effluent limitations or current effluent quality, whichever is 

lower (in the case of facilities with such limitations) or current effluent quality (in the case of facilities 
Total Maximum Daily Load for Total Mercury in the Middle/Lower Savannah River, GA February 28, 2001

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subject to mercury characterization requirements). 

• The permitting authority will establish the shortest reasonable period of time for compliance with 

permit limitations and conditions based on this TMDL. 

• The State of Georgia will require those facilities rated as “minor municipal” and “minor industrial” 

facilities to monitor for mercury using the version of EPA Method 1631 then in effect to verify 

whether or not they have a added mercury. (State of Georgia Rules and Regulations for Water 

Quality Control, April 2000, Chapter 391-3-6-.06, and January 1995 Reasonable Potential 

Procedures).

This TMDL incorporates wasteload load allocations in the form of Option B only because each of the 

following factors is present: 

• this TMDL addresses mercury, which EPA believes is best handled at these levels through waste 

minimization rather than through end-of-pipe treatment;

• the NPDES point sources, in the aggregate contribute only 1% of the total current mercury loadings 

to the Savannah River;

• EPA has reasonable assurance that implementation of pollution controls required under current law 

will result in reductions sufficient to achieve the load allocation of 32.5 kg/year assigned to air

sources, thus authorizing a cumulative wasteload allocation of 0.3 kg/year.

• if the Savannah River were currently attaining water quality standards, mercury discharges from the 

identified NPDES point sources at levels equivalent to the cumulative wasteload allocation of 0.3 

kg/year would not cause or contribute to an exceedance of applicable water quality standards for 

mercury as interpreted by EPA in the River; and

• the recent adoption of EPA Method 1631 Revision B makes it difficult for EPA to state with 
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69

certainty how many of the point sources identified in this TMDL actually discharge a net addition of 

mercury at levels exceeding 2.8 ng/l. Under these circumstances, waste characterization is a 

reasonable first step.

10.3. State and Federal Responsibility

EPA intends to undertake the following responsibilities under this TMDL:

1. Review “major” NPDES permits and other identified “minor” NPDES permits for facilities located 

in the watershed of the segments of the Savannah River that are covered by this Phase 1 TMDL;

2. Take the lead on further characterization of air sources; and 

3. Take the lead on revising the TMDL.

EPA expects Georgia to undertake the following responsibilities: 

1. Identify the “major” NPDES facilities affected by this TMDL;

2. Identify other NPDES “minor” facilities affected by this TMDL which have the potential for a 

significant concentration of mercury in their effluent; 

3. Modify the NPDES permits for the facilities identified in 1 and 2 above to reflect the conditions as 

identified in Section 10.2.;

4. Determine the frequency and duration of the mercury characterization to be undertaken by the 

facilities identified in 1 and 2 above;

5. Determine the due date and objectives for the mercury minimization plan to be developed by the 

facilities in 1 and 2 above that are shown to be discharging mercury in excess of 2.8 nanograms/liter 

through the mercury characterization effort in 4 above; 
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6. Review the mercury minimization plans and determine the plan’s acceptability as identified in 5 

above;

7. Assure that mercury minimization plans are implemented as expeditiously as practicable; and

8. Adopt numeric water quality criteria for mercury for protection of public health in accordance with 

40 C.F.R. §131.11(b).

11. Assumptions with Respect to Loadings from South

Carolina

This TMDL reflects EPA’s assumption that concentrations of mercury in the South Carolina portion of the 

Savannah River will meet the applicable Georgia water quality standards at the South Carolina-Georgia 

border. The water quality standard that applies to this TMDL is Georgia’s narrative water quality criterion 

for toxics, which provides that Georgia waters shall be free from toxic substances in amounts harmful to 

humans. EPA has interpreted that standard as 2.8 ng/l. As a technical matter, meeting Georgia’s standard 

at the border is important because there is no hydrological difference between the South Carolina and 

Georgia portions of the Savannah River. Moreover, the fish travel freely across the border; they may be 

exposed to mercury in South Carolina, but be consumed by individuals in Georgia. Therefore, an important 

assumption of this TMDL is that concentrations of mercury at the Georgia/South Carolina border will not 

exceed 2.8 ng/l. 

EPA believes that this assumption is reasonable because the TMDL already takes into account substantial 

reductions from South Carolina air sources located within the Savannah River watershed and within a 100 

km radius of the watershed. The TMDL’s gross load allocation to air sources also already accounts for 

emissions that EPA expects to remain from South Carolina air sources after application of air pollution 

controls. In addition, with respect to NPDES point sources in South Carolina, EPA believes that loadings 

from South Carolina can meet Georgia’s water quality standard as interpreted by EPA for mercury at the 
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71

border if South Carolina employs either of the two-wasteload allocation approaches discussed above for 

Georgia NPDES point sources. This TMDL expressly assumes that limitations on South Carolina point 

sources that reflect either approach will meet the requirements of 40 C.F.R. § 122.4(d), which states that 

South Carolina may not issue an NPDES permit unless it includes conditions that ensure compliance with 

Georgia’s water quality standards. For a discussion of the bases for EPA’s assumption, see the Response 

to Comments.
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12. Appendix A 

Appendix-A Savannah River Hg TMDL.PDF
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 Appendix B – List of NPDES Facilities in Middle/Lower Savannah Basin

Facility NPDES Permit # County

A&M Products Inc. GA0036811 Jefferson

Air Liquid America GA0046230 Chatham

Albion Kaolin Company GA0002470 Richmond

Atlantic Wood Ind. GA0047783 Chatham

Augusta Butler Creek GA0037621 Richmond

Budget Inn Savannah GA0034096 Chatham

Central of Georgia R/R GA0002381 Chatham

Citgo Asphalt Refining Co. GA0004332 Chatham

Coastal Water & Sewer Co. GA02-234 Effingham

Columbia Co. Crawford GA0031984 Columbia

Columbia Co. Detention Center GA02-002 Columbia

Columbia Co. Health Dept. GA0049735 Columbia

Columbia Co. Little River GA0047775 Columbia

Columbia Co. Reed GA0031992 Columbia

Crawford Eastside WPCP GA0033693 Oglethorpe

CSR Aggregates Richmond GA0037231 Richmond

Dearing LAS GA02-007 McDuffie

DHR Gracewood Hospital GA0022161 Richmond

DHR Gracewood Sch. WPCP GA0047279 Columbia

DIT SRA#112/I-75 Visitor GA0033278 Chatham

DIT Sylvania Welcome Stat GA0030287 Screven

DOT Rest Areas #62 & #63 GA0047325 Columbia

DSM Chemicals Augusta, Inc. GA0002160 Richmond

E.M. Industries Inc. GA0034355 Chatham

ECC International Wrens GA0048101 Jefferson

Effingham Elem School GA0046990 Effingham

Engelhard Corp Chatham GA0048330 Chatham

Fort James Company GA0046973 Effingham

GAF Corporation Savannah Plant GA0003841 Chatham

Garden City WPCP GA0031038 Chatham

Georgia Pacific Corp. GA0047007 Chatham

Georgia Pacific Gypsum GA0001961 Chatham

Georgia Power Vogtle GA0026786 Burke

Grovetown LAS GA02-222 Columbia

Gulfstream Aerospace Corp GA0003255 Chatham

Harlem WPCP GA0020389 Columbia

Hephzibah WPCP GA0049433 Richmond

Hercules GA0026867 Chatham

Herty Foundation Savannah GA0002402 Chatham

Hiltonia LAS GA02-033 Screven

Intermarine USA GA0003671 Chatham

International Paper Co. GA0037711 Burke

International Paper Co. GA0002801 Richmond

Kemira GA0003646 Chatham

King Division of Spartan Mills GA0004049 Richmond

Martin Marietta Aggr. GA0002909 Richmond

Martin Marietta Matl Inc GA0037346 Columbia
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Olin Corporation Augusta GA0003719 Richmond

PCS Nitrogen Fertilizer LP GA0002071 Richmond

PCS Nitrogen Fertilizer LP GA0002356 Chatham

Peridot Chemicals GA0002925 Richmond

Pooler/Bloomingdale Req GA0047066 Chatham

Richmond Co Spirit Cr. GA0047147 Richmond

Rincon GA0046442 Effingham

Sardis WPCP GA0020893 Burke

Savannah Elec Effingham GA0003883 Effingham

Savannah Elec Riverside GA0003751 Chatham

Savannah Elec Wentworth GA0003816 Chatham

Savannah Electric & Power Co GA0047708 Chatham

Savannah President St GA0025348 Chatham

Savannah Sugar Refinery GA0003611 Chatham

Savannah Travis Field GA0020427 Chatham

Savannah Wilshire/Windsor GA0020443 Chatham

Savannah Yacht Club GA0033189 Chatham

Solutia Inc GA0002178 Richmond

South Carolina Electric GA0003786 Richmon

Southern Aggregates Columbia GA0036790 Columbia

Southern States Phosphorous & Fert GA0002437 Chatham

Springfield GA0020770 Effingham

Stone Container Corp GA0002798 Chatham

Sylvania Yarns Systems Inc WQ-IP-047 Screven

Thermal Ceramics Inc GA0002488 Richmond

Thiel Kaolin Hobbs GA0032981 Warrant

Tybee Island GA0020061 Chatham

Union Camp Corporation GA0001988 Chatham

USA Ft. Gordon GA0003484 Richmond

USA Hunter AFB STP GA0027588 Chatham

Waynesboro WPCP GA0020231 Burke

Wrens WPCP GA0021857 Jefferson
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